Kral T A, Brink K M, Miller S L, McKay C P
Department of Biological Sciences, University of Arkansas, Fayetteville, USA.
Orig Life Evol Biosph. 1998 Jun;28(3):311-9. doi: 10.1023/a:1006552412928.
It is possible that the first autotroph used chemical energy rather than light. This could have been the main source of primary production after the initial inventory of abiotic organic material had been depleted. The electron acceptor most readily available for use by this first chemoautotroph would have been CO2. The most abundant electron donor may have been H2 that would have been outgassing from volcanoes at a rate estimated to be as large as 10(12) moles yr-1, as well as from photo-oxidation of Fe+2. We report here that certain methanogens will consume H2 down to partial pressures as low as 4 Pa (4 x 10(-5) atm) with CO2 as the sole carbon source at a rate of 0.7 ng H2 min-1 microgram-1 cell protein. The lower limit of pH2 for growth of methanogens can be understood on the basis that the pH2 needs to be high enough for one ATP to be synthesized per CO2 reduced. The pH2 values needed for growth measured here are consistent with those measured by Stevens and McKinley for growth of methanogens in deep basalt aquifers. H2-consuming autotrophs are likely to have had a profound effect on the chemistry of the early atmosphere and to have been a dominant sink for H2 on the early Earth after life began rather than escape from the Earth's atmosphere to space.
最早的自养生物有可能利用的是化学能而非光能。在初始的非生物有机物质储备耗尽之后，这可能一直是初级生产的主要能量来源。最早的这种化能自养生物最容易利用的电子受体可能是二氧化碳。最丰富的电子供体或许是氢气，它会以估计高达每年10¹²摩尔的速率从火山中逸出，同时也来自亚铁离子的光氧化反应。我们在此报告，某些产甲烷菌会以二氧化碳作为唯一碳源，将氢气消耗至分压低至4帕斯卡（4×10⁻⁵ 个标准大气压），消耗速率为每分钟每微克细胞蛋白0.7纳克氢气。产甲烷菌生长所需的氢气分压下限可以这样理解，即氢气分压需要足够高，以便每还原一个二氧化碳分子就能合成一个三磷酸腺苷（ATP）。此处测得的产甲烷菌生长所需的氢气分压值与史蒂文斯和麦金利在深层玄武岩含水层中测得的产甲烷菌生长所需的氢气分压值一致。消耗氢气的自养生物很可能对早期大气的化学性质产生了深远影响，并且在生命起源之后成为早期地球上氢气的主要汇，而非从地球大气逃逸到太空。
