Ma `lumot

Qadimgi yerning anaerob sharoitlarida siyanobakteriyalar qanday omon qolishi mumkin edi?

Qadimgi yerning anaerob sharoitlarida siyanobakteriyalar qanday omon qolishi mumkin edi?



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Men siyanobakteriyalar haqida o'qiyotgan edim va ular taxminan 2,3 milliard yil oldin atmosferani kislorod bilan to'ldirgan birinchi organizmlar ekanligini bilib oldim, lekin keyin ularning o'zlari aerob ekanligini angladim va aerob organizm qanday yashay olishini tushunolmadim. birinchi navbatda kislorod kam bo'lgan atmosfera butun atmosferani to'ldiradigan va deyarli barcha anaerob organizmlarning yo'q bo'lib ketishiga olib keladigan etarli kislorod hosil qiladi.


Birinchi siyanobakteriyalar, ehtimol, anaerob edi va bu masala zamonaviy tadqiqotlarning dolzarb mavzusi bo'lib tuyuladi. Yaqinda nashr etilgan tadqiqota Turli xil siyanobakteriyalar genomlarining filogenetik tahlilini o'tkazgan tadqiqotchilar:

Ushbu ma'lumotlardan olingan eng aqlli xulosa shundan iboratki, siyanobakteriyalarning oxirgi umumiy ajdodi kisloroddan foydalanmagan va uchta sinf [siyanobakteriyalar] ajralib chiqqandan keyin mustaqil ravishda aerob nafas olishga erishgan. Ota-bobolarining siyanobakteriyalarida aerob nafas olishning yo'qligi shuni ko'rsatadiki, erta Erdagi abiotik kislorod manbalari fotosintez natijasida hosil bo'lgan kislorod paydo bo'lgunga qadar uning evolyutsiyasiga imkon berish uchun etarli emas edi.

Malumot

a Soo, Rochelle M. va boshqalar. "Siyanobakteriyalarda kislorodli fotosintez va aerob nafas olishning kelib chiqishi to'g'risida". Fan 355.6332 (2017): 1436-1440 (http://web.gps.caltech.edu/~wfischer/pubs/Sooetal2017.pdf)


Taxminlarga ko'ra, Yer 4,6 milliard yil oldin (milliard yil oldin) paydo bo'lgan. Eng qadimgi meteoritlar taxminan shu vaqtga to'g'ri keladi, ammo Yer ancha vaqt davomida yarim erigan bo'lar edi. Cho'kindi jinslarning tarkibiy qismlari qariyb 4,4 milliard yilga to'g'ri keladi, bu Yer o'z tarixida okeanlarning paydo bo'lishiga imkon beradigan darajada soviganligini ko'rsatadi (Nemchin, 2006).

Qadimgi jinslar qatlamlaridan olingan uglerod izotoplari ko'rsatkichlari er yuzida hayot 3,8 milliard yil oldin va ehtimol 3,85 milliard yil oldin mavjud bo'lgan degan xulosani tasdiqlaydi (Mojzsis, 1996). 3,8 milliard yil oldin bo'lgan jinslarda tirik organizmlar mavjudligini ko'rsatadigan uglerod izotoplari nisbati mavjud. Uglerodning izotoplari deb ataladigan turli shakllari mavjud. Tirik mavjudotlar ma'lum bir uglerod izotopidan (12 C) foydalanadi va ikkinchi izotopni (13 C) chiqarib tashlaydi, ammo minerallarning hosil bo'lishida ularning hech biri kamsitilmaydi. Tog' jinslari cho'kindilarida uglerod nisbatlarini 10 000 dan ortiq tahlildan so'ng, sifat farqi kuzatiladigan faqat bitta davr mavjud. Taxminan 3,8 milliard yil oldin, ma'lum cho'kindilardagi uglerod izotoplarining nisbati hayot yo'qligidan tirik mavjudotlar bilan bog'liq bo'lganlarga o'zgargan. Ushbu tahlil shuni ko'rsatadiki, tirik mavjudotlar Yerda 3,85 milliard yil oldin mavjud bo'lgan. Uglerod izotoplarining bu o'zgarishi sayyorada suyuq suv paydo bo'lganidan ko'p o'tmay sodir bo'ldi (Brocks, 1999 Schidlowski, 1988 Golland, 1997). Yoshi 3,5 milliard yil bo'lgan jinslar ham hayot mavjudligini ko'rsatadi (Akai, 2006).

Grenlandiyaning Isua tog' jinslarida 3,8 milliard yoshga to'g'ri keladigan kichik organik moddalarning "tolga qoldiqlari" mavjud. Ularning ichida organik moddalar mavjud bo'lsa-da va ularning bo'linishi (xamirturush kabi tomurcuklanma) misollari mavjud bo'lsa-da, ular tirik hujayralar yoki jonsiz mikrosferalar ekanligi aniq emas (Pflug, 1979 Roedder, 1981 Bridgwater, 1981 Dunlop, 1978) .

Mars jinslarida organik moddalar bo'lgan "nanofossillar" topilgan. Ba'zilar bu mayda tuzilmalar Marsdagi ibtidoiy organizmlar tomonidan yaratilgan deb o'ylashadi (garchi ko'pchilik bu talqinga rozi bo'lmasa ham) (Trevors, 2003b). Qadimgi mikroblarning biomineralizatsiyasi natijasida mikrofosil hosil bo'lishi ko'pincha metall ionlarining hujayra yuzasiga qo'shilishi natijasidir. "Nanobakteriyalar" minerallashgan mikroblarning qismlari bo'lishi mumkin, masalan, poya va pufakchalar (Sautam, 1999). Hajmi 0,1 dan 0,5 mikrongacha bo'lgan va har bir-uch kunda takrorlanadigan nanobakteriyalar odamlarda polikistik buyrak kasalligi kabi ba'zi kasalliklarga ta'sir qiladi (Ciftcioglu, 2002).

Ko'pchilik fotoalbomlar cho'kindi jinslar deb nomlanuvchi jinslarda topilgan. Ma'lum bo'lgan eng qadimgi cho'kindi jins konlari G'arbiy Grenlandiyaning 3,8 milliard yil oldin Isua hosil bo'lishidir. Ma'lum bo'lgan eng qadimgi jinslarning yoshi atigi 4,0 milliard yil ekanligini hisobga olsak, 3,8 milliard yil avvalgidan sezilarli darajada katta bo'lgan cho'kindi jinslar topilishi dargumon. Isuada ma'lum bo'lgan qazilma toshlar mavjud bo'lmasa-da, bu jinsdagi uglerod nisbati fotosintetik mikroblarning qoldiqlarini o'z ichiga olgan keyingi jinslarda topilganlarga o'xshaydi (McClendon, 1999).

Juda kichik uglerodli mikroyapılar, ehtimol abiotik bo'lgan Isuadagi 3,8 milliard yillik jinslarda ma'lum. Avstraliyadagi eng qadimgi mikrofosillarning yoshi 3,5 milliard yil (Pflug, 2001 McClendon, 1999). Meteoritlardagi mikro tuzilmalar ibtidoiy mikroblarning mikrofossillariga o'xshaydi. Meteoritlarning organik tuzilmalari va musbat ionlarining massa spektrlarining o'lchamlarini kimyoviy tahlil qilish prekembriy mikrofossillarini o'z ichiga olgan tog 'qatlamlarining tahlillariga o'xshash bo'lishi mumkin. Murchison meteoriti ikki qavatli lipid membranasi bilan o'ralgan kichik tuzilmalarga ega edi. Ushbu kichik tuzilmalar 10 nm dan 1 mikrongacha bo'lgan spiral va sferik uglerodli mikro tuzilmalar va kengligi 2-20 nm va uzunligi 1-2 nm bo'lgan birliklardan tashkil topgan filamentlar shaklida bo'lishi mumkin. Ushbu kichik organik tuzilmalarni qanday talqin qilish kerak? Garchi ba'zilar o'zlarini tirik yoki hayotning kashshoflari deb bilishsa-da, hech bo'lmaganda ular er yuzida va kosmosda abiotik sharoitda hujayra qoldiqlariga o'xshash organik mikrotuzilmalar paydo bo'lishi mumkinligini ko'rsatadilar (Pflug, 2001).

Bakteriyalar okeanning chuqurligida, yer ostida va hatto tosh ichida ham bo'lishi mumkinligini hisobga olsak, hayotning kelib chiqishi haqida o'ylashda bu muhitlarni hisobga olish kerak. Bakteriyalar dala shpati (Smit, 1999) kabi ba'zi tosh minerallari kanallarida mavjud bo'lishi mumkin. Yer yuzida taxminan 4-6 x 10 30 prokariotik hujayralar mavjud bo'lib, ularning umumiy uglerod massasi o'simliklarning umumiy uglerod massasi bilan tengdir. yer (350-550 Pg 1 Pg = 10 12 kg). Aniq qiymatlar noma'lum bo'lsa-da, tuproqda va okean tubida juda ko'p prokaryotlar mavjud. Chuqur suvli qatlamlar va neft bilan bog'liq bo'lgan suv bir millilitrda mingdan milliongacha mikrobni o'z ichiga olishi mumkin. Er ostida 2000 metr chuqurlikda 400 000 dan ortiq mikrob / kub santimetr va 3000 metr chuqurlikda 300 000 dan ortiq mikrob / kub santimetr topilgan (Whitman, 1998). Okean tubi ostidagi toshlarda juda ko'p mikroblar yashaydi. Mikroblar dengiz tubida 1,6 km dan ortiq chuqurlikda, yoshi 100 million yildan ortiq bo'lgan cho'kindilarda topilgan. Bu mikroblarning ba'zilari metabolik faol va bo'linishda edi. Ular orasida metanning anaerob oksidlanishida omon qolgan arxiyalar bor. Ba'zilar er yuzidagi prokaryotlarning 2/3 qismi dengiz ostidagi jinslarda yashaydi, deb taxmin qilishgan (Roussel, 2008). Eng ibtidoiy zamonaviy bakteriyalarning aksariyati chuqur dengiz gidrotermal teshiklarida yashaydi. Tarixdan oldingi gidrotermal teshiklar qazilma qoldiqlaridan ma'lum, shu jumladan turli xil bakterial fauna bilan bog'liq bo'lgan prekembriy teshiklari (Li, 2006 Kempbell, 2006).

Bugungi kunda er yuzida ikki xil turdagi hujayralar mavjud. Prokaryotik hujayralar zamonaviy bakteriyalar bilan ifodalanadi va hujayraning eng oddiy turi hisoblanadi. Prokaryotik hujayralar kichik (odatda eukaryotik hujayralardan 10 000 marta kichik) va organellalar deb ataladigan membrana bilan bog'langan ichki bo'linmalarga ega emas. Zamonaviy bakteriyalarning ikkita asosiy bo'limi mavjud: eubakteriyalar va arxebakteriyalar (yoki arxeya). Eubakteriyalar odamlar tez-tez uchraydigan bakteriyalarning ko'p qismini tashkil qiladi, arxeya esa erning eng og'ir muhitlarida yashaydi. So'nggi yillarda arxeylarga qiziqish ortib bormoqda, chunki ular va murakkabroq eukaryotik hujayralar (masalan, inson tanasini tashkil etuvchi) o'rtasidagi o'xshashlik.

Prokaryotik (bakterial) hujayralarning birinchi qoldiqlari 3,5 va 3,4 milliard yil oldin ma'lum. Bu bakteriyalar fotosintetik edi (kislorod ishlab chiqarmasa ham), shuning uchun oddiyroq fotosintetik bo'lmagan bakteriyalar bundan oldin rivojlangan bo'lishi mumkin (Schopf, 1987 Beukes, 2004). Tarixdan oldingi fotosintetik bakteriyalar balandligi 30 futga yetadigan stromatolitlar deb ataladigan katta tepaliklar hosil qilgan. Bugungi kunda Avstraliyada bakterial stromatolitlar mavjud va qazilma qoldiqlari shuni ko'rsatadiki, ular bir vaqtlar butun dunyoda keng tarqalgan. Stromatolitlar hatto arxeozoy erasidan 3 qit'adan ma'lum bo'lib, ularning ba'zilari 3,5 milliard yildir. Yosh stromatolitlar bakteriyalar tomonidan ishlab chiqarilgan bakterial qoldiqlarni o'z ichiga oladi (Lowe, 1980 Walter, 1980). Qadimgi stromatolitlar ham bakteriyalar tomonidan hosil qilingan bo'lishi mumkin (ularning mikroskopik tuzilishi, suv osti holati, biotik stromatolitlarga o'xshashligi shundan dalolat beradi), ammo ba'zilari abiotik (geologik kuchlar natijasida bakteriyalarsiz) hosil bo'lishi mumkin (Grotzinger, 1996). . Prekembriy stromatolitlari quyida tasvirlangan.

Geokimyoviy dalillar shuni ko'rsatadiki, metan hosil qiluvchi bakteriyalar er yuzida 3,46 milliard yil avval mavjud bo'lgan. Ular ishlab chiqargan metan, quyosh energiya ishlab chiqaradigan bir vaqtda sayyorani isitishda (metan kuchli issiqxona gazi ekanligini hisobga olib) muhim rol o'ynashi mumkin edi (Ueno, 2006). Arxeozoyning so'nggi davridagi uglevodorodlar bakteriya va arxeyalarning erta biosferaga hissa qo'shganligini ko'rsatadi. Arxeya tomonidan ishlab chiqarilgan metan, yosh quyoshning energiya ishlab chiqarishi zamonaviy miqdordan kamroq bo'lsa, suvning suyuqligini saqlaydigan issiqxona gazlariga hissa qo'shgan bo'lishi mumkin (Ventura, 2007).

Bakteriyalar hayot tarixidagi kamida birinchi 1,5 milliard yil davomida er yuzida ma'lum bo'lgan yagona aholidir. Genetik taqqoslashlar shuni ko'rsatadiki, eng qadimgi, eng ibtidoiy bakteriya nasl-nasabi anaerob bo'lgan va kislorod ishtirokida omon qolish qobiliyati turli avlodlarda alohida rivojlangan. Fotosintez asosiy eubakterial nasllarning yarmida mavjud bo'lgan qadimiy jarayon bo'lib ko'rinadi (shu jumladan fotosintetik ajdodlar fotosintetik bo'lmagan avlodlarni keltirib chiqargan ko'rinadi (Fox, 1980). Gidrotermal teshiklar prekembriydagi mikrob jamoalarini qo'llab-quvvatlagani ma'lum. (Kampbell, 2006). Eng ibtidoiy zamonaviy bakteriyalarning ko'pchiligi chuqur dengiz gidrotermal teshiklarida yashaydi. Tarixdan oldingi gidrotermal teshiklar qazilma qoldiqlaridan ma'lum, shu jumladan turli xil bakterial fauna bilan bog'liq bo'lgan prekembriy ventslari (Li, 2006 2007).

Dengiz suvi bir millilitrda o'rtacha 100 000 dan ortiq mikrobni va okeandagi taxminiy jami 3,6 x 10E29 mikrobni o'z ichiga oladi. Mikroblarning bu massasi (shu jumladan bakteriyalar, arxeya, protistlar va zamburug'lar) okean biomassasining katta qismini tashkil qiladi, taxminan 3 x 10 E17 g. Ushbu mikroblarning xilma-xilligi ilgari taxmin qilinganidan ancha katta ekanligi isbotlangan (Sogin, 2006).

Uch milliard yil oldin, siyanobakteriyalar ("ko'k yashil suv o'tlari" nomi bilan yaxshi ma'lum bo'lgan bakteriyalar turi) fotosintez paytida kislorod chiqaradigan evolyutsiyaga aylandi. Birinchi bakteriyalar, ehtimol, fotosintezda kislorod o'rniga vodorod va vodorod sulfidini chiqargan. 2,7 milliard yil oldin, stromatolit hosil qiluvchi mikroblar kislorodli fotosintezdan foydalanganga o'xshaydi (Buick, 1992). Atmosferadagi kislorod miqdori 2,4 va 2,2 milliard yil oldin sezilarli darajada oshdi (Rye, 1998). Siyanobakteriyalar mavjudligining molekulyar dalillari 2,7 milliard yillik jinslarga va ixtisoslashgan hujayralarga 2,1 milliard yillik jinslardan ma'lum (Tomitani, 2006). 2,2 milliard yil oldin, siyanobakteriyalar zanjirlari kattalashgan hujayralar bilan mavjud edi (ular zamonaviy turlarda bo'lgani kabi, azot almashinuvi kabi vazifalar uchun ixtisoslashgan bo'lishi mumkin), bu hujayra ixtisoslashuvining birinchi ma'lum namunasidir (Nagy, 1974 Schopf).

Eng qadimgi atmosferada kislorod gazi unchalik ko'p bo'lmagan. Fotosintezdan oldin, atmosferada juda kam miqdorda bo'lgan tog' jinslarining parchalanishi natijasida juda ko'p kislorod so'rilgan bo'lar edi. Kislorod gazining yagona manbai suv molekulalarining quyosh nuri ta'sirida ajralishi bo'lar edi (Des Marais, 2000). Buni o'sha paytda hosil bo'lgan cho'kindilarni kuzatishda ko'rish mumkinki, metallar zanglamagan va kislorod ishtirokida hosil bo'lgan minerallar yo'q. Arxeozoy davrining temir konlari anoksik muhitdan dalolat beradi (Lascelles, 2007). 2,1 milliard yil oldin atmosferada birinchi marta temirni zanglash uchun etarli miqdorda kislorod bor edi va taxminan 1,8 milliard yil oldin kislorod sezilarli miqdorda temirni oksidlantirdi. Bu vaqtda kislorodning boshqa belgilari ham paydo bo'ladi, masalan, 1,7 milliard yil avvalgi steran biomarkerlari va taxminan 1,6 milliard yil oldin oksidlangan oltingugurt konlari. Atmosferadagi kislorod darajasi prekembriy davrining oxiriga kelib, Ediakar faunasi diversifikatsiya qilinishidan oldin ortadi (Kaufman, 2007 Canfield, 2007).

Birinchi bakteriyalarda kislorodning halokatli reaktiv shakllari bilan shug'ullanadigan fermentlar (masalan, peroksidaza kabi) bo'lmaganligi sababli, kislorod havoning birinchi ifloslanishini ifodalagan va bakteriyalar orasida ko'plab yo'q bo'lib ketishiga olib kelgan bo'lar edi. Bugungi kunda kislorod borligida yashay olmaydigan ko'plab bakteriyalar mavjud.

Fotosintetik mikroorganizmlarning qazilma qoldiqlari juda yaxshi, siyanobakteriyalar taxminan 2,5 milliard yil avvaldan Kembriy davrigacha mustahkam bo'lgan. Tog' jinslarida qolgan organik molekulalar fotoalbom xronologiyasini qo'llab-quvvatlaydi. (Masalan, 2-metil bakteriyopanepoliollar faqat siyanobakteriyalardan ma'lum va uning jinslarda mavjudligi jins hosil bo'lganida siyanobakteriyalar mavjud bo'lganligini ko'rsatadi.) (Marais, 1992 Logan, 1999 de Duve, 1996)


Siyanobakteriyalar bizga iqlimga moslashishni o'rgatishi mumkin Agar okean iliq bo'lsa, siyanobakteriyalar yoki "ko'k yashil suv o'tlari" kamroq ozuqa moddalari bilan omon qolishi mumkin.

Iqlim o'zgarishi tufayli okeanlar isinmoqda va bu eng kichik planktondan tortib eng katta orkinosgacha bo'lgan barcha okean hayotiga ta'sir qiladi. Okeandagi hayot tarmog'i murakkab va shuning uchun aynan qaysi ekotizimlarga ta'sir qilishi va ular qanchalik o'zgarishi hozirda qizg'in o'rganilmoqda. Oziq-ovqat tarmog'ining asosi bo'lgan va kislorod ishlab chiqaruvchi fitoplanktonga ushbu o'zgaruvchan muhit qanday ta'sir qilishini tushunish ayniqsa muhimdir. Agar fitoplankton kamaysa yoki tarqalish o'zgarsa, baliqchilik ham ovning kamayishi yoki baliqning hududdan butunlay chiqib ketishini ko'rishi mumkin.

Siyanobakteriyalar ko'p sonli, qadimiy va keng tarqalgan fitoplankton turidir. Ular Yerning qadimiy atmosferasini yuqori karbonat angidriddan (CO2 ) kislorod miqdori yuqori bo'lib, biz bilgan hayot evolyutsiyasiga yo'l ochadi. Bitta siyanobakteriya mikroskopikdir, ammo sharoit qulay bo'lsa, ular kosmosdan ko'rinadigan juda katta koloniyalar yoki gullashlari mumkin.

Ushbu tadqiqotda tadqiqotchilar siyanobakteriyalar uchun muhim ozuqa bo'lgan temirning ko'pligi siyanobakteriyalar turlarining o'sish tezligiga qanday ta'sir qilishini aniqlashni xohlashdi. Trichodesmium erythraeum turli haroratlarda. Trixodesmiy ekologik jihatdan muhim siyanobakteriyalardir, chunki u azot gazini organik azotga aylantiradi, keyinchalik azotni biriktirish deb ataladigan jarayon yordamida boshqa hayvonlar tomonidan ishlatilishi mumkin. Faqat bir nechta turlar azotni noorganik shakldan boshqa tirik organizmlar foydalanishi mumkin bo'lgan shaklga o'zgartirishi mumkin, bu azot fiksatorlarini juda muhim qiladi. Ko'pincha fitoplanktonni o'rganishda isinish va ozuqa moddalarining ko'pligi o'sishga qo'shimcha ravishda ta'sir qiladi, deb taxmin qilinadi. Bu shuni anglatadiki, ularning o'sishi harorat va ozuqa moddalarining ko'pligi ta'sirida o'zgaradi. Biroq, tadqiqotchilar ushbu tadqiqotda bu biroz murakkabroq ekanligini ko'rsatdi. Haroratning ko'tarilishi fitoplankton metabolizmiga va kimyoviy reaktsiyalarga ko'proq energiya ta'minlab, o'sish tezligiga qo'shimcha o'zgarishlarni keltirib chiqarishi mumkin.

Ushbu tajriba uchun Janubiy Kaliforniya universiteti va bir nechta Xitoy universitetlari olimlari o'sdi Trixodesmiy 22 ℃ dan 35 ℃ gacha (maksimal omon qolish mumkin bo'lgan harorat) yoki temirning ortiqcha miqdori yoki temirning past darajasi. Ular planktonning o'sish tezligini kuzatdilar va radioaktiv temir birikmalari yordamida hujayralardagi temir iste'molini kuzatdilar.

Temir ko'p bo'lganda, siyanobakteriyalar 27 ℃ da eng tez o'sdi, ammo temir cheklangan bo'lsa, maksimal o'sish tezligi 32 ℃ da sodir bo'ldi. Cheklovchi ozuqa moddasi bo'lgan fosforda ham shunga o'xshash holat topilgan Trixodesmiy temir ko'p bo'lgan joylarda o'sishi. Bu shuni anglatadiki, okeanlar maksimal 35 ℃ gacha isishi bilan temirning past darajalari muammosiz bo'lib qoladi va siyanobakteriyalar bir xil haroratda cheksiz temir bilan tez o'sishi mumkin. Harorat oshishi bilan ularning azot fiksatsiya tezligi ham barqaror sur'atda oshdi. Tadqiqotchilar, siyanobakteriyalar temir kam bo'lgan issiqroq sharoitda tezroq o'sishini nazariya qilmoqdalar, chunki atrof-muhit iliq bo'lsa, hujayralar ichidagi reaktsiyalar tezroq boradi va fermentlar (temir o'z ichiga olgan) tezroq ajralib chiqadi va qayta biriktiriladi. Bu shuni anglatadiki, kamroq miqdordagi temir (va fosfor) hujayra ichida bir xil miqdordagi ishni bajarishi mumkin, chunki issiqroq haroratda hamma narsa tezroq ketadi.

Olimlar kelajakdagi iliqroq okeanda okean mahsuldorligini bashorat qilish uchun modellarni ishlab chiqishganda, ko'pchilik bu kabi ta'sirlarni hisobga olmaydi va shuning uchun biomassa va azot fiksatsiyasi miqdorini kam baholaydi. Boshqa tadqiqotlar shuni ko'rsatdiki, yuqori CO2 azot fiksatsiyasi tezligini ham oshiradi, lekin bu jarayon temir bilan ham cheklangan. Ushbu tadqiqot yuqori haroratlarda kamroq temir talab qilinishini ko'rsatganligi sababli, CO ning ortishi bilan azot fiksatsiyasi yanada kuchayishi ehtimoldan yiroq.2 darajalari. Ushbu tadqiqot tadqiqotchilarining fikriga ko'ra, agar siyanobakteriyalarning boshqa turlari ham xuddi shunday reaksiyaga kirishsa, 2100 yilda azot fiksatsiyasi o'rtacha 21,5% ga oshadi. Foiz geografik hududga qarab katta farq qiladi, ammo ba'zi hududlarda 35 ℃ dan yuqori bo'lishi taxmin qilinmoqda, ya'ni ko'pchilik fitoplanktonlar umuman yashay olmaydi.

Haddan tashqari isib ketmaydigan hududlarda bu azot fiksatsiyasi okean isishining ba'zi salbiy oqibatlarini oldini olishga yordam beradi. Yer okeanlarining isishi oqimlarni kamaytirishi va shuning uchun okeanlarni qatlamlarga ajratishi taxmin qilinmoqda. Bu organik azot kabi ozuqa moddalarining chuqurlikdan yer yuzasiga normal almashinuvini oldini oladi. Shunday qilib, siyanobakteriyalar tomonidan noorganik azotning har qanday ortib borayotgan fiksatsiyasi, agar jiddiy tabaqalanish sodir bo'lsa, er usti suvlarini zarur organik azot bilan ta'minlashi mumkin.

Oziq-ovqat tarmog'i bazasidagi har qanday o'zgarish hamma narsani oldindan aytish qiyin bo'lgan usullar bilan o'zgartiradi. Shu sababli, iqlim o'zgarishining o'simliklar va fitoplanktonlarga ta'sirini tushunish kelajak nima olib kelishini bilish uchun eng katta ahamiyatga ega.


Erning dastlabki atmosferasi: yangilanish

Rensselaer Politexnika Instituti qoshidagi NAI ’s Nyu-York Astrobiologiya Markazi olimlari Yerdagi eng qadimgi minerallardan Yer tug'ilgandan so'ng tez orada mavjud bo'lgan atmosfera sharoitlarini tiklash uchun foydalanganlar. Nature jurnalining joriy sonida e'lon qilingan topilmalar sayyoramizning qadimiy atmosferasi paydo bo'lganidan ko'p o'tmay qanday bo'lganligining birinchi to'g'ridan-to'g'ri dalilidir va sayyorada hayot paydo bo'lgan atmosfera turiga oid ko'p yillik tadqiqotlarni bevosita shubha ostiga qo'yadi. .

Olimlar Yer atmosferasi yaratilganidan atigi 500 million yil o'tgach, ilgari taklif qilinganidek, metan bilan to'ldirilgan cho'l emasligini, aksincha bizning hozirgi atmosferamiz sharoitlariga ancha yaqinroq bo'lganini ko'rsatdi. "Hadean magmalarining oksidlanish holati va erta Yer atmosferasiga ta'siri" nomli maqoladagi topilmalar bu sayyorada hayot qanday va qachon boshlangani va koinotning boshqa joylarida boshlanishi mumkinligini tushunishimizga ta'sir qiladi.

O'nlab yillar davomida olimlar erta Yer atmosferasi juda qisqargan, ya'ni kislorod juda cheklangan deb hisoblashgan. Bunday kislorod kambag'al sharoitlar zararli metan, uglerod oksidi, vodorod sulfidi va ammiak bilan to'ldirilgan atmosferaga olib keladi. Bugungi kunga qadar bu halokatli atmosfera kokteylidan Yerdagi hayot qanday qurilgan bo'lishi mumkinligi haqida keng tarqalgan nazariyalar va tadqiqotlar mavjud.

Endi, Rensselaer olimlari bu atmosfera taxminlarini rad etishmoqda, bu topilmalar Yerdagi sharoitlar bu turdagi atmosferaning shakllanishiga emas, balki kislorodga boy birikmalar hukmron bo'lgan atmosferaga yordam beradi. bizning hozirgi atmosferamiz - suv, karbonat angidrid va oltingugurt dioksidi.

"Biz hozir aniq aytishimiz mumkinki, Yerdagi hayotning kelib chiqishini o'rganayotgan ko'plab olimlar shunchaki noto'g'ri atmosferani tanlaganlar", dedi Bryus Uotson, Rensselaerdagi fan instituti professori.

Topilmalar Yer atmosferasi uning yuzasida vulqon faolligidan ajralib chiqadigan gazlar natijasida hosil bo'lgan degan keng tarqalgan nazariyaga asoslanadi. Bugungi kunda, Yerning dastlabki kunlaridagi kabi, Yer chuqurligidan oqib chiqayotgan magma tarkibida erigan gazlar mavjud. Bu magma sirtga yaqinlashganda, bu gazlar atrofdagi havoga chiqariladi.

"Ko'pchilik olimlar magmadan chiqadigan gazning atmosferaga asosiy kirishi bo'lganini ta'kidlaydilar", dedi Uotson. "Atmosferaning tabiatini "dastlab" tushunish uchun atmosferani ta'minlaydigan magmalarda qanday gaz turlari borligini aniqlashimiz kerak edi."

Magma Yer yuzasiga yaqinlashganda, u otilib chiqadi yoki qobiqda to'xtab qoladi, u erda atrofdagi jinslar bilan o'zaro ta'sir qiladi, soviydi va qattiq toshga aylanadi. Bu muzlatilgan magmalar va ular tarkibidagi elementlar Yer tarixida tom ma'noda muhim bosqichlar bo'lishi mumkin.

Muhim bosqichlardan biri tsirkondir. Vaqt o'tishi bilan eroziya va subduktsiya natijasida vayron bo'ladigan boshqa materiallardan farqli o'laroq, ba'zi tsirkonlar deyarli Yerning o'zi kabi eskidir. Shunday qilib, tsirkonlar tom ma'noda sayyoramizning butun tarixini aytib berishi mumkin - agar siz to'g'ri so'rashni bilsangiz.

Olimlar bu qadimiy tsirkonlarni hosil qilgan magmalarning oksidlanish darajasini aniqlashga harakat qilishdi, bu esa Yer tarixida birinchi marta chiqarilgan gazlar qanchalik oksidlanganligini aniqlashdi. Astrobiologiya markazining doktorlik dissertatsiyasidan keyingi tadqiqotchisi Dastin Trailning so'zlariga ko'ra, oksidlanish darajasini tushunish yomon botqoq gazi va suv bug'lari va karbonat angidrid aralashmasi o'rtasidagi farqni aniqlab berishi mumkin.

"Tsirkonni yaratgan magmalarning oksidlanish darajasini aniqlash orqali biz oxir-oqibat atmosferaga tushadigan gazlar turlarini aniqlashimiz mumkin", dedi Trail.

Buning uchun Trail, Uotson va ularning hamkasbi, postdoktorlik tadqiqotchisi Nikolas Teylbi laboratoriyada turli oksidlanish darajalarida tsirkonlarning shakllanishini qayta yaratdilar. Ular laboratoriyada tom ma'noda lava yaratdilar. Ushbu protsedura keyinchalik tabiiy tsirkonlar bilan taqqoslanadigan oksidlanish o'lchagichni yaratishga olib keldi.

Ushbu jarayon davomida ular sirkonlarda seriy deb ataladigan noyob Yer metalining kontsentratsiyasini qidirdilar. Seriy muhim oksidlanish o'lchovidir, chunki uni ikkita oksidlanish darajasida topish mumkin, biri ikkinchisiga qaraganda ko'proq oksidlanadi. Tsirkonda ko'proq oksidlangan turdagi seriyning kontsentratsiyasi qanchalik yuqori bo'lsa, ular hosil bo'lgandan keyin atmosfera shunchalik oksidlangan bo'ladi.

Kalibrlashlar hozirgi sharoitga yaqinroq oksidlanish darajasiga ega bo'lgan atmosferani aniqlaydi. Topilmalar Yerdagi hayotning kelib chiqishi bo‘yicha kelajakdagi tadqiqotlar uchun muhim boshlanish nuqtasi bo‘lib xizmat qiladi.

"Bizning sayyoramiz butun hayot o'ynagan sahnadir", dedi Uotson. “Biz bu bosqich nima ekanligini bilmagunimizcha, Yerdagi hayot haqida gapira olmaymiz. Va kislorod sharoitlari juda muhim edi, chunki ular hosil bo'lishi mumkin bo'lgan organik molekulalarning turlariga qanday ta'sir qiladi.

Hozirgi vaqtda hayot nafas olayotgan, yashaydigan va gullab-yashnagan atmosfera bo'lishiga qaramay, bizning hozirgi oksidlangan atmosfera hayot uchun ajoyib boshlanish nuqtasi sifatida tushunilmagan. Metan va uning kislorodga kam bo'lgan hamkasblari noorganik birikmalardan hayotni qo'llab-quvvatlovchi aminokislotalar va DNKga o'tish uchun ko'proq biologik salohiyatga ega. Shunday qilib, Uotsonning fikricha, uning guruhining kashfiyoti, ehtimol, hayot uchun qurilish bloklari Yerda yaratilmagan, balki galaktikaning boshqa joyidan yetkazilgan degan nazariyalarni jonlantirishi mumkin.

Biroq, natijalar anaerob organizmlardan aerob organizmlargacha bo'lgan hayot yo'li haqidagi mavjud nazariyalarga zid emas. Natijalar eng qadimgi atmosferada uglerod, vodorod va oltingugurtni o'z ichiga olgan gaz molekulalarining tabiatini aniqlaydi, ammo ular havodagi erkin kislorodning ancha keyinroq ko'tarilishiga hech qanday oydinlik kiritmaydi. Trail ma'lumotlariga ko'ra, biologik mexanizmlar orqali atmosferada kislorod to'planishi uchun hali ham ko'p vaqt bor edi.

NASA Astrobiologiya dasturidan eng soʻnggi yangiliklar, voqealar va imkoniyatlarni olish uchun roʻyxatdan oʻting.


Tadqiqot mikroorganizmlarning og'ir muhitda qanday yashashini ko'rsatadi

Chili shimolidagi Atakama cho'lida, er yuzidagi eng qurg'oqchil joylardan biri, mikroorganizmlar o'zlari mustamlaka qilgan jinslardan suv olish orqali mavjud bo'lishlari mumkin.

Kaliforniya universiteti, Irvin, Jons Xopkins universiteti va Kaliforniya universiteti, Riversayd tadqiqotchilari tomonidan armiya tomonidan moliyalashtirilgan loyiha fotosintetik mikroblarning qadimgi guruhi bo'lgan ba'zi siyanobakteriyalarning og'ir muhitda omon qolishi mexanizmlari haqida chuqur tushunchaga ega bo'ldi.

nashr etilgan yangi tushunchalar Milliy Fanlar Akademiyasi materiallari, suv ko'p bo'lmagan joylarda hayot qanday gullab-yashnashi mumkinligini isbotlang, jumladan Marsda - va qurg'oqchil mintaqalarda yashovchi odamlar bir kun kelib mavjud minerallardan hidratsiya olishlari mumkinligini ko'rsating.

"Armiya ekstremal muhitga yaxshi moslashgan mikroorganizmlardan materiallar sintezi va ushbu og'ir maydonlarda energiya ishlab chiqarish kabi yangi ilovalar uchun qanday foydalanish mumkinligiga katta qiziqish bildiradi", dedi doktor Robert Kokoska, armiya tadqiqot boshqarmasi dastur menejeri. AQSh armiyasining jangovar qobiliyatlarini rivojlantirish qo'mondonligining Armiya tadqiqot laboratoriyasining elementi. "Ushbu tadqiqot cho'lda yashovchi ushbu mahalliy mikroblar tomonidan ko'plab ekologik muammolarga duch kelganda o'zlarining hayotiyligini saqlab qolish uchun qo'llaniladigan ishlab chiqilgan dizayn strategiyalarini ochish uchun qimmatli maslahatlar beradi."

Dala va laboratoriya tajribalari orqali tadqiqot guruhi butun dunyodagi cho'llarda uchraydigan quriydigan siyanobakteriyalarning Chroococcidiospsis turi va kaltsiy sulfat asosidagi mineral suv bo'lgan gipsning o'zaro ta'siriga e'tibor qaratdi. Kolonizatsiya qiluvchi hayot shakllari yupqa tosh qatlami ostida mavjud bo'lib, bu ularga Atakamaning haddan tashqari harorati, yuqori quyosh nurlanishi va kuchli shamollardan himoya qiladi.

Hammuallif Jocelyne DiRuggiero, JHU biologiya kafedrasi dotsenti gips namunalarini yig'ish uchun uzoq cho'lga sayohat qildi va ularni AQShdagi laboratoriyalariga olib keldi. U mikroorganizmlar topilishi mumkin bo'lgan kichik bo'laklarni kesib, materiallarni tahlil qilish uchun UCIga yubordi.

Tadqiqotning eng hayratlanarli topilmalaridan birida tadqiqotchilar mikroorganizmlar o'zlari egallagan jinslarning tabiatini o'zgartirishini bilib oldilar. Suvni chiqarib, ular materialning fazaviy o'zgarishiga olib keladi - gipsdan anhidritga, suvsizlangan mineralga.

DiRuggieroning so'zlariga ko'ra, nashr etilgan ish uchun turtki, materialshunoslik va muhandislik bo'yicha UCI post-doktori Vey Huang Atakamada to'plangan gips namunalarida angidrit va siyanobakteriyalar kontsentratsiyasining bir-biriga mos kelishini ko'rsatadigan ma'lumotlarni aniqlaganida paydo bo'ldi.

"Mikroblar kolonizatsiya qilingan tosh hududlarini tahlil qilishimiz kaltsiy sulfatning suvsizlangan fazasini aniqladi, bu ular tirik qolish uchun toshdan suv olishlarini ko'rsatdi", dedi Devid Kisailus, bosh muallif va UCI materialshunoslik va muhandislik professori. "Biz bu gipotezani tasdiqlash uchun boshqa nazorat ostida tajribalar o'tkazmoqchi edik."

Keyin DiRuggiero jamoasi organizmlarga kuponlar deb ataladigan yarim millimetrli jinslar kublarini ikki xil sharoitda, biri suv borligida, yuqori namlikli muhitni taqlid qilish uchun, ikkinchisi esa butunlay quruq holda kolonizatsiya qilishga ruxsat berdi. Namlik o'rtasida gips anhidrit fazasiga o'tmagan.

"Ularga toshdan suv kerak emas edi, ular uni atrofdan olishdi", dedi Kisailus. "Ammo ular og'ir sharoitlarda qo'yilganda, mikroblarning gipsdan suv olishdan boshqa iloji yo'q edi, bu materialda bu fazaviy o'zgarishlarni keltirib chiqardi."

Kisailus jamoasi biologik va geologik hamkasblar o'rtasidagi o'zaro ta'sirni o'rganish uchun ilg'or mikroskopiya va spektroskopiya kombinatsiyasidan foydalangan va organizmlar organik kislotalarni o'z ichiga olgan bioplyonkani chiqarib tashlash orqali mayda konchilar kabi materialga kirib borishini aniqladilar, dedi Kisailus.

Huang Raman spektrometri bilan jihozlangan o'zgartirilgan elektron mikroskopdan foydalangan holda, organizmlar kislotadan toshga ma'lum kristallografik yo'nalishlarda - faqat ma'lum tekisliklarda, kaltsiy va sulfat ionlari yuzlari orasidagi suvga oson kirishlari mumkin bo'lgan kirish uchun foydalanganligini aniqladi.

Kisailusning ta'kidlashicha, loyiha mikrobiologlar va materialshunoslar o'rtasidagi fanlararo tadqiqotlarning ajoyib namoyishi bo'lib, bir kun kelib ilmiy kashfiyotlarning boshqa shakllariga eshiklarni ochishi mumkin.

"Olimlar uzoq vaqt davomida mikroorganizmlar minerallardan suv olishi mumkinligiga shubha qilishgan, ammo bu uning birinchi namoyishi", dedi DiRuggiero. "Bu hayotning quruq chegarasida yashovchi mikroorganizmlar uchun ajoyib omon qolish strategiyasi va u boshqa joylarda hayot izlashimizga yo'l-yo'riq ko'rsatadi."

Tadqiqotchilarning ta'kidlashicha, ushbu tadqiqot Armiya tadqiqot laboratoriyasining sintetik biologiyadagi sa'y-harakatlariga foyda keltirishi mumkin.

Laboratoriyaning biotexnologiya bo'limidan doktor Metyu Perisin: "Ushbu topilmalar laboratoriyamizning qiziqishini uyg'otdi, chunki mikrobial omon qolish mexanizmlari og'ir harbiy muhitda bioishlab chiqarish yoki platformalarni sezish uchun ishlatilishi mumkin".

Sarlavha tasviri - Shimoliy Chilidagi Atakama cho'lida, Yer yuzidagi eng qurg'oqchil joylardan biri, mikroorganizmlar qattiq shamol va quyosh nurlanishidan himoyalanish uchun yupqa tosh qatlamlari ostida yashaydi. Suv cheklangan bo'lsa-da, bu jinslar ichida strukturaviy element sifatida saqlanadi. Kredit: Devid Kisailus, Kaliforniya universiteti - Irvine


Kislorod ishlab chiqaruvchi siyanobakteriyalar murakkab hayotni qanday osonlashtirdi

2,43 milliard yil oldin. Manba, fanga ko'ra, siyanobakteriyalarni fotosintez qilish edi. Lekin nega bu juda muhim burilish juda kech sodir bo'ldi? Siyanobakteriyalar hayoti, tosh namunalari shuni ko'rsatadiki, GOE dan kamida 300 million yil oldin mavjud edi. Achim Herrmann, who is researching the spread of early cyanobacteria in his doctoral thesis at TU Kaiserslautern, is hot on the trail for answers. His current research paper has now been published in the journal Tabiat bilan aloqa.

“There are many scientific theories that intertwine to explain why the proliferation of cyanobacteria required for the GOE was delayed,” explains Herrmann, who is working on his doctorate with Michelle Gehringer in Geomicrobiology. “For example, they may have originated in fresh water, which covered then, as now, only a fraction of Earth’s surface. It wasn’t until they adapted to saltier waters and finally inhabited the open ocean that they were able to form sufficient amounts of biomass to cause a global change in Earth’s atmosphere.” Another theory is that the iron-rich ocean water may have initially been toxic to the photosynthesizing bacteria. Iron had accumulated in the marine environment predominantly in the form of highly soluble, reduced iron(II) ions during the Earth’s then oxygen free “Archean” age.

In his research Herrmann built upon the iron toxin hypothesis. “We wanted to check whether iron(II) inhibits not only modern Cyanobacteria but also more primitive, marine strains, specifically Pseudanabaena sp. PCC7367 and Synechococcus sp. PCC7336, in their growth and photosynthetic activity,” said the biologist.

It quickly became apparent how crucial the experimental setup is. In already established systems where the bacteria are cultivated in closed glass bottles without oxygen, they demonstrated almost no growth: “The biological activity was very low in both strains, and almost completely suppressed in Synechococcus,” Herrmann says. The solution: “A custom-built anaerobic workstation from the TUK metal workshop, in whose chambers the composition of the atmosphere can be regulated fully and automatically,” he says. “Using this setup, we cultivated the cyanobacteria in large laboratory bottles with gas-permeable lids to allow gas exchange. The oxygen they produced was regularly removed from the system, and carbon dioxide was kept constant at proposed Archean atmospheric levels. Thus, we were able to realize a shallow marine oxygen oasis as implied in Archean rock samples.”

As expected, the cyanobacteria “felt more comfortable” in the more authentic environment. But what happened when iron was injected in increasing concentrations? The bacteria from the Pseudanabaena strain grew consistently well, but more slowly than in the control system. In contrast, the Synechococcus strain clearly decreased its rate of cell division as iron increased. The oxygen produced primarily oxidized the dissolved Fe(II) ions instead of escaping into the atmosphere. And the oxygen production rate for both strains reached significantly higher values in the anoxically adjusted experimental environment than in the control setup with an oxygenated atmosphere, like that which surrounds us today. This would suggest that modern day atmospheric oxygen levels impair photosynthesis when compared to the anoxic atmosphere of Earth’s past.

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In addition, the formation of green rust, a mix of Fe(II) and oxidized iron Fe(III), was shown only in the culture system developed by Herrmann. The formation of green rust was accompanied by a strong decrease of biological activity, probably caused by iron oxides encrusting the bacterial cells. During the Archean, the formation of such green rust may have contributed decisively to banded iron formations, the most important source of iron ore today.

Finally, Herrmann changed the experimental scenario once again and simulated iron conditions for a tidal zone. Iron was added at night, when oxygen concentrations dropped towards zero due to no photosynthetic activity. The result: growth slowed significantly in both strains, but never stopped completely. This indicates that an Archean oxygen oasis could also have tolerated the influx of iron-rich water during the night. Here, too, the formation of green rust occurred, but could be further oxidized quickly and thus did not bring growth to a standstill.

All in all, Herrmann’s research has filled in more gaps in the puzzle of Earth’s history. He was able to illustrate for both cyanobacterial strains how the iron cycle might have proceeded in an Archean oxygen oasis, and that smaller colonized areas would probably have been sufficient for the start of the GOE due to the higher oxygen production rates. He has also developed a concept for growing cyanobacteria that better represents Archaean living conditions.

“I hope that with my research paper, I can help us better understand how our oxygen rich atmosphere was able to evolve in the first place,” Herrmann says.

Provided by: Technische Universität Kaiserslautern

More information: A. J. Herrmann et al. Diurnal Fe(II)/Fe(III) cycling and enhanced O2 production in a simulated Archean marine oxygen oasis. Tabiat bilan aloqa (2021). DOI: 10.1038/s41467-021-22258-1

Rasm: Achim Herrmann is researching the spread of early cyanobacteria.
Kredit: Koziel/TUK


Niches of extant prokaryotic phototrophs

The co-occurrence of cyanobacteria and anoxygenic phototrophs is common in euxinic lakes, phototrophic microbial mats, hot springs and hypersaline lagoons where sufficient fluxes of reduced compounds are available to support anoxygenic photosynthesis. The ability to harvest light and tolerance to oxygen are most often cited as the key factors governing occurrence of phototrophs in ecological niches along stratified water columns and mats. For instance, green and purple sulfur bacteria (GSB and PSB) are found in most sunlit, sulfidic environments, where PSB are generally found at more shallow depths in the water column or mats (Overmann and Garcia-Pichel, 2006 Meyer va boshqalar., 2011). GSB have lower light requirements and are generally less tolerant to oxygen. In addition, GSB have higher affinity for sulfide than PSB, conferring a competitive advantage over PSB when reduced sulfur compounds are limiting (Van Gemerden, 1984 Pringault va boshqalar., 1999). In contrast, a combination of sulfide and temperature appears to inhibit photosynthesis in alkaline hot springs above ∼70°C (Cox va boshqalar., 2011 Boyd va boshqalar., 2012 ).

Extant members of the phylum Siyanobakteriyalar are metabolically diverse and include species that can perform anoxygenic photosynthesis in the presence of high sulfide (Cohen va boshqalar., 1975a,b ) in environments where sulfide is present in the photic zone (Jørgensen va boshqalar., 1983 1986 ). Some cyanobacteria can also use hydrogen as an electron donor (Cohen va boshqalar., 1986 ), perform sulfide-dependent nitrogen fixation (Belkin va boshqalar., 1982 ), and/or grow photoheterotrophically (Kenyon va boshqalar., 1972 Rippka va boshqalar., 1979 ). This phenotypic diversity enables cyanobacteria to tolerate a variety of environmental extremes, and results in their ability to occupy niches in almost any environment where light is available, including many in which they are important primary producers. For example, benthic cyanobacterial mats in Solar Lake, Sinai, a hypersaline pond, undergo drastic yearly changes in temperature, salinity, oxygen, light and H2S. Cyanobacterial mats in Solar Lake are dominated by metabolically diverse cyanobacteria such as Osilatoriya species that are capable of anoxygenic photosynthesis and phototaxis (Cohen va boshqalar., 1975a Krumbien va boshqalar., 1977 ). Xuddi shunday, Phormidium species survive freezing and desiccation in Antarctica (Taton va boshqalar., 2003 ) and persist in the low O2 conditions in the Middle Island Sinkhole of Lake Huron (Voorhies va boshqalar., 2012 ).

In some extant environments such as photic zones where oxygen and sulfide coexist, the ecological niches of anoxygenic phototrophs and cyanobacteria can overlap (Klatt va boshqalar., 2011 2013 ). For instance, in some stratified lakes, the oxic/anoxic interface is shallow and supports dense layers of anoxygenic phototrophs. These conditions mimic those thought to be present in areas of the Proterozoic oceans, especially along continental shelf margins. In these systems today, anoxygenic photosynthesis can be the main source of primary production (Van Gemerden and Mas, 1995 ).


Introduction to the Cyanobacteria

Cyanobacteria are aquatic and photosynthetic, that is, they live in the water, and can manufacture their own food. Because they are bacteria, they are quite small and usually unicellular, though they often grow in colonies large enough to see. They have the distinction of being the oldest known fossils, more than 3.5 billion years old, in fact! It may surprise you then to know that the cyanobacteria are still around they are one of the largest and most important groups of bacteria on earth.

Many Proterozoic oil deposits are attributed to the activity of cyanobacteria. They are also important providers of nitrogen fertilizer in the cultivation of rice and beans. The cyanobacteria have also been tremendously important in shaping the course of evolution and ecological change throughout earth's history. The oxygen atmosphere that we depend on was generated by numerous cyanobacteria during the Archaean and Proterozoic Eras. Before that time, the atmosphere had a very different chemistry, unsuitable for life as we know it today.

The other great contribution of the cyanobacteria is the origin of plants. The chloroplast with which plants make food for themselves is actually a cyanobacterium living within the plant's cells. Sometime in the late Proterozoic, or in the early Cambrian, cyanobacteria began to take up residence within certain eukaryote cells, making food for the eukaryote host in return for a home. This event is known as endosimbioz, and is also the origin of the eukaryotic mitochondrion.

Because they are photosynthetic and aquatic, cyanobacteria are often called "blue-green algae". This name is convenient for talking about organisms in the water that make their own food, but does not reflect any relationship between the cyanobacteria and other organisms called algae. Cyanobacteria are relatives of the bacteria, not eukaryotes, and it is only the xloroplast in eukaryotic algae to which the cyanobacteria are related.

Click on the buttons below to find out more about the Cyanobacteria.

ning tasvirlari Nostok va Osilatoriya provided by the University of Wisconsin Botanical Images Collection.

For more information about cyanobacteria on the web, visit Cyanosite, a webserver dedicated to cyanobacterial research.

Information about the ecology of fresh-water cyanobacteria is available from the Soil and Water Conservation Society of Metro Halifax.

The Tree of Life has a preliminary page on the Cyanobacteria, with some very nice pictures.


Salt of the Early Earth

The next time you reach for that bag of salty chips, think for a moment about salt and life. Humans need a certain amount of salt it is necessary for the delivery of nutrients, the transmission of nerve impulses, and the contractions of the heart and other muscles. In fact, every form of life on this planet needs salt. But why should that be? What role did salt play in the evolution of life on Earth?

Scientists have long assumed that life originated in the sea. If life did spring from salt water, that could explain why all organisms use salt. But Paul Knauth, an astrobiologist with Arizona State University, says while we always assume that life came from the ocean, this theory has never been proven. He suggests we need to consider the possibility that life originated in fresh water.

“Fresh” water is somewhat of a misnomer – all fresh water bodies still do contain some salt. Non-marine salt levels are less than 1 part per thousand, while marine salt levels are around 35 parts per thousand. But when life first appeared around 3.5 billion years ago, the ocean was much saltier than it is today. Estimates of the early ocean’s salinity range between 1.2 to 2 times present-day salinity.

“Life is stressed today in the current ocean, so one can speculate that higher salinities make things even tougher,” says Knauth.

Salt does seem to have played some sort of role in the origin of life – it is the precise concentration of salts that is at issue. In constructing the steps that led to the first life form, many scenarios invoke the concentration of salts through evaporation.

“In the early saltier ocean, this would lead to a real devil’s brew,” says Knauth.

However, non-marine bodies of water have a wide range of changing environments. Knauth says that some of these fresh water environments probably had the optimal salinity for the kinds of molecular assembly proposed for the origin of life.

Shiladitya DasSarma, a professor at the University of Maryland Biotechnology Institute, Center of Marine Biotechnology, agrees that life could have originated in fresh water pools. So long as these pools had a certain amount of organic molecules, prebiotic evolution could have occurred. However, DasSarma thinks that life also could have begun in the early salty ocean. He has found that, due to the low water activity of hypersaline brines, macromolecules can form from organic molecules. A macromolecule is a very large molecule, such as a protein or other polymer.

The macromolecules in these salty waters, combined with other molecules, could have formed membranes capable of Darwinian evolution (and thus be classified as a life form).

Liquid water began accumulating on the surface of the Earth about 4 billion years ago, forming the early ocean. Most of the ocean’s salts came from volcanic activity or from the cooled igneous rocks that formed the ocean floor.

This volcanic activity also created island chains that grew over time. Tectonic plate movement caused these islands to collide, forming thecores of the continents. The continents developed fresh water lakes and ponds through rainfall and other meteorological processes.

Soon after both salty water and fresh water were available, life originated. The oldest fossils we have are from 3.5 billion-year-old cyanobacteria, but life probably emerged even earlier than that. Genetic analysis has shown that the archaean branch of life came first, appearing sometime before bacteria.

Immense bloom of a halophilic (“salt-loving”) archaean species at a salt works near San Quentin, Baja California Norte, Mexico.
Credit: UCMP

One form of archaea is adapted to live in high-salt environments. Known as “halophiles” (“salt lovers”), these organisms live in wet salty environments such as the Dead Sea and Utah’s Great Salt Lake. If halophiles were found to be the most ancient archaeans, the origin of life would point toward very salty water.

The specific antiquity of halophiles is not currently known, but because they breathe oxygen they are not believed to be one of the earliest forms of archaea. Oxygen wasn’t a major component of the Earth’s atmosphere until anaerobic organisms like cyanobacteria began producing it. However, DasSarma has some evidence that halophiles may lie very deeply in the tree of life.

DasSarma and his team have recently sequenced the genome of an extreme halophile called Halobacterium species NRC-1. DasSarma says that when the genes of Halobacterium NRC-1 are compared to other organisms, this halophile seems to be the most ancient archaean.

“This is very unexpected,” says DasSarma. “The small ribosomal RNA-based trees pointed to halophiles as recent relatives of a class of anaerobic archaea called methanogens, which have very simple metabolism involving methane production from inorganic gases.”

DasSarma says the close relationship between halophiles and methanogens never made sense because they do not share physiological capabilities: Halophiles need oxygen methanogens do not. But it turns out halophiles are able to produce energy without oxygen in two ways: from the degradation of arginine, and by using the photosynthetic molecule bacteriorhodopsin.

Perhaps these two methods of non-oxygen energy production are the last remnants from the halophile’s earlier, anaerobic days. As the Earth’s oxygen levels rose 2 billion years ago, the gas would have killed off many anaerobic organisms. In a process called “lateral gene transfer,” halophiles may have borrowed genes from aerobic bacteria in order to survive this increase in oxygen.

“Our analysis of genes in halophiles suggest common ancestry with many bacterial genes, for example, those involved in aerobic respiration,” says DasSarma. “Whether these are recently acquired by lateral gene transfers or have common ancestry with bacteria is currently being analyzed.”

The rise of oxygen as an atmospheric gas changed the face of life on Earth. Many life forms died out, while other life forms adapted to the new gas. But Knauth says the early ocean wouldn’t have absorbed very much of this oxygen. If the ocean was warm in its early days – and Knauth believes that the ocean 3.5 billion years ago was like hot tap water – then the combination of high temperature and high salinity would have resulted in an ocean with very little dissolved oxygen.

Oxygen-use has been linked with the development of complex life forms. Therefore, Knauth says the ancient, anoxic sea would have housed only the simpler organisms like anaerobic bacteria, while aerobic organisms and other complex life forms evolved in fresh water. But another dramatic environmental change was on the horizon: the formation of the continents led to a process that reduced the amount of salt in the ocean. Low-lying continental areas were sometimes flooded by ocean waters, but these shallow seas evaporated relatively quickly – in about 100 million years. The minerals left behind formed large salt basins, and this sequestered salt resulted in lower ocean salinity.

As the ocean cooled and salt basins began to form, the ocean would have been able to absorb more oxygen. This oxygen absorption opened up a new environmental niche for aerobic organisms, and the sea would have seen an explosion of new life forms. In fact, if the salt basins formed around 540 million years ago, Knauth believes ocean salt levels could have had a hand in the Cambrian Explosion.

Scientists still have not figured out what triggered the enormous increase in the diversity of life in the Cambrian era. But salt basins, forming in a brief period of time and decreasing the salinity of the oceans, would have had a profound impact on life.

“The currently favored view for the major control on the Cambrian explosion of life is that atmospheric oxygen levels built up until metazoan life was possible,” says Knauth. “These larger organisms need higher oxygen levels to survive. My point is that it is dissolved oxygen that is critical here, not just the atmospheric level. The arrival of big salt deposits on the continents in the latest Precambrian could have been one of the key factors that allowed the shallower oceans to finally oxygenate enough for metazoans to take to the sea.”

Halophilic life may have been transfered to Earth from Mars meteors.
Kredit: NASA

The role of salt in the origin and evolution of life is still an open question. To find answers, Knauth says scientists need to take a closer look at the depositional environments of sedimentary rocks that hold Precambrian microfossils. But what if the answer is not to be found in the rocks of Earth? If halophiles turn out to be the most ancient life form, perhaps we need to look at the red rocks of Mars for our answers.

Mars originally had much more salt than the Earth, and when Mars lost 50 to 90 percent of its water through evaporation it became even saltier. The Panspermia theory says that life originated elsewhere and then was transferred to Earth by meteors. If the earliest life forms were halophiles, says Knauth, then perhaps we are really Martians.

DasSarma finds the idea of halophilic life on Mars a fascinating concept. He says it may be possible to look for such life on Mars today.

“If indeed Mars is salty and life could have evolved there, it may still be trapped in brine inclusions within salt crystals,” says DasSarma. “Another property of earthly halophiles that may have some bearing on their ability to survive is that these organisms are extremely resistant to solar radiation, and therefore would be excellent candidates for interplanetary travel.”

DasSarma suggests it may be possible to discover what halophiles were like in their early days by studying salt bitterns: hypersaline brines that are left after the commercial production of salt. Like the early ocean, salt bitterns are anoxic as well as extremely salty.

“It is intriguing that the intracellular salt concentrations of modern halophiles resemble the potassium-enriched, sodium-depleted bitterns remaining after the harvesting of marine salt,” says DasSarma.

DasSarma says it may be possible to create a “prebiotic soup” of organic and inorganic components along with brine from a bittern. This mixture perhaps could allow growth of modern halophiles exhibiting some of their primordial capabilities.

Knauth, meanwhile, is working on the question of whether life evolved in the ocean and adapted to lower salinity environments, or whether life evolved in fresh water and then adapted to life in the oceans. He is looking at the fossil record of various non-marine environments to try to answer this question, and has found some very promising sites in Australia.

“Currently I’m exploring life on land in the Precambrian,” says Knauth. “I’m looking at non-marine environments to see if the fossil record indicates whether life could have originated in that environment rather than in the sea, as we’ve always thought.”


Blue-green algae

Tahririyatimiz siz yuborgan narsalarni ko'rib chiqadi va maqolani qayta ko'rib chiqish yoki yo'qligini aniqlaydi.

Blue-green algae, deb ham ataladi siyanobakteriyalar, any of a large, heterogeneous group of prokaryotic, principally photosynthetic organisms. Cyanobacteria resemble the eukaryotic algae in many ways, including morphological characteristics and ecological niches, and were at one time treated as algae, hence the common name of blue-green algae. Algae have since been reclassified as protists, and the prokaryotic nature of the blue-green algae has caused them to be classified with bacteria in the prokaryotic kingdom Monera.

Like all other prokaryotes, cyanobacteria lack a membrane-bound nucleus, mitochondria, Golgi apparatus, chloroplasts, and endoplasmic reticulum. All of the functions carried out in eukaryotes by these membrane-bound organelles are carried out in prokaryotes by the bacterial cell membrane. Some cyanobacteria, especially planktonic forms, have gas vesicles that contribute to their buoyancy. Chemical, genetic, and physiological characteristics are used to further classify the group within the kingdom. Cyanobacteria may be unicellular or filamentous. Many have sheaths to bind other cells or filaments into colonies.

Cyanobacteria contain only one form of chlorophyll, chlorophyll a, a green pigment. In addition, they contain various yellowish carotenoids, the blue pigment phycobilin, and, in some species, the red pigment phycoerythrin. The combination of phycobilin and chlorophyll produces the characteristic blue-green colour from which these organisms derive their popular name. Because of the other pigments, however, many species are actually green, brown, yellow, black, or red.

Most cyanobacteria do not grow in the absence of light (ya'ni, they are obligate phototrophs) however, some can grow in the dark if there is a sufficient supply of glucose to act as a carbon and energy source.

In addition to being photosynthetic, many species of cyanobacteria can also “fix” atmospheric nitrogen—that is, they can transform the gaseous nitrogen of the air into compounds that can be used by living cells. Particularly efficient nitrogen fixers are found among the filamentous species that have specialized cells called heterocysts. The heterocysts are thick-walled cell inclusions that are impermeable to oxygen they provide the anaerobic (oxygen-free) environment necessary for the operation of the nitrogen-fixing enzymes. In Southeast Asia, nitrogen-fixing cyanobacteria often are grown in rice paddies, thereby eliminating the need to apply nitrogen fertilizers.

Cyanobacteria range in size from 0.5 to 60 micrometres, which represents the largest prokaryotic organism. They are widely distributed and are extremely common in fresh water, where they occur as members of both the plankton and the benthos. They are also abundantly represented in such habitats as tide pools, coral reefs, and tidal spray zones a few species also occur in the ocean plankton. On land, cyanobacteria are common in soil down to a depth of 1 m (39 inches) or more they also grow on moist surfaces of rocks and trees, where they appear in the form of cushions or layers.

Cyanobacteria flourish in some of the most inhospitable environments known. They can be found in hot springs, in cold lakes underneath 5 m of ice pack, and on the lower surfaces of many rocks in deserts. Cyanobacteria are frequently among the first colonizers of bare rock and soil. Various types of associations take place between cyanobacteria and other organisms. Certain species, for example, grow in a mutualistic relationship with fungi, forming composite organisms known as lichens.

Cyanobacteria reproduce asexually, either by means of binary or multiple fission in unicellular and colonial forms or by fragmentation and spore formation in filamentous species. Under favourable conditions, cyanobacteria can reproduce at explosive rates, forming dense concentrations called blooms. Cyanobacteria blooms can colour a body of water. For example, many ponds take on an opaque shade of green as a result of overgrowths of cyanobacteria, and blooms of phycoerythrin-rich species cause the occasional red colour of the Red Sea. Cyanobacteria blooms are especially common in waters that have been polluted by nitrogen wastes in such cases, the overgrowths of cyanobacteria can consume so much of the water’s dissolved oxygen that fish and other aquatic organisms perish.

This article was most recently revised and updated by Chelsey Parrott-Sheffer, Research Editor.


Could cyanobacteria terraform Mars?

That blue-green algae has implications for astrobiology.

The bacteria that 3.5 billion years ago were largely responsible for the creation of a breathable atmosphere on Earth could be press-ganged into terraforming other planets, research suggests. A team of biologists and chemists from Australia, the UK, France and Italy has been investigating the ability of cyanobacteria – also known as blue-green algae – to photosynthesise in low-light conditions.

Cyanobacteria are some of the most ancient organisms around, and were responsible, though photosynthesis, for converting the Earth’s early atmosphere of methane, ammonia and other gases into the composition it sustains today.

The photochemistry used by the microbes is pretty much the same as that used by the legion of multicellular plants that subsequently evolved. The process involves the use of red light. Most plants are green because chlorophyll is bad at absorbing energy from that part of the visible light spectrum, and thus reflects it.

Light itself, however, is a critical component for photosynthesis, which is why plants (and suitably equipped bacteria) fail to grow in very dark environments. Just how dark such environments need to be before the process becomes impossible was the focus of the new research.

The team of scientists, which included Elmars Krausz from the Australian National University in Canberra, tested the ability of a cyanobacterial species called Chroococcidiopsis thermalis to photosynthesise in low light.

Previously it had been widely thought that the necessary photochemistry shut down at a light wavelength of 700 nanometres – a point known as the “red limit”.

Krausz and his colleagues, however, found that C. thermalis continued to photosynthesise at wavelengths up to 750 nanometres. The finding not only represents a significant extension of the low-light photosynthesis limit, but also describes a system that can function using much less biological fuel. The researchers call it an “unprecedented low-energy photosystem”.

The key, the scientists discovered, lies in the presence of previously undetected long-wavelength chlorophylls, which perform the necessary charge separation. The researchers traced the origin of these chlorophylls back to the C. thermalis genome, and discovered that it was located in a specific gene cluster that is common in many cyanobacterial species – suggesting that the ability to surpass the red limit is common.

To Krausz this low-light ability holds promise for the use of cyanobacteria as frontline terraforming agents. Establishing colonies on other planets would set in motion an atmospheric transformation that should – eventually – result in human-friendly conditions.

Of course, if some astrobiological theories are correct, cyanobacteria (or, at least, similar lifeforms) may already exist on other planets – in which case their ability to survive in harsh low-light conditions suggests a new target for detection.

“This might sound like science fiction, but space agencies and private companies around the world are actively trying to turn this aspiration into reality in the not-too-distant future,” says Krausz.

“Photosynthesis could theoretically be harnessed with these types of organisms to create air for humans to breathe on Mars.

“Low-light adapted organisms, such as the cyanobacteria we’ve been studying, can grow under rocks and potentially survive the harsh conditions on the red planet.”

Tadqiqot jurnalda chop etilgan Fan.

Andrew Masterson

Andrew Masterson is a former editor of Cosmos.

Badiiy emas, ilmiy faktlarni o‘qing.

Faktlarni tushuntirish, dalillarga asoslangan bilimlarni qadrlash va so'nggi ilmiy, texnologik va muhandislik yutuqlarini namoyish qilish uchun hech qachon muhim vaqt bo'lmagan. Kosmos odamlarni ilm-fan olami bilan bog'lashga bag'ishlangan Avstraliya Qirollik Instituti tomonidan nashr etilgan. Moliyaviy hissalar, qat'i nazar, katta yoki kichik bo'lishidan qat'i nazar, bizga ishonchli fan ma'lumotlariga dunyo eng zarur bo'lgan vaqtda kirish imkonini beradi. Iltimos, bugun xayriya qilish yoki obuna sotib olish orqali bizni qo'llab-quvvatlang.

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Videoni tomosha qiling: Bola huquqlari konvensiyasi 1-qism (Avgust 2022).