Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA.
Astrobiology. 2013 May;13(5):476-82. doi: 10.1089/ast.2012.0913.
Humic substances (HS) are high-molecular-weight complex refractory organics that are ubiquitous in terrestrial and aquatic environments. While resistant to microbial degradation, these compounds nevertheless support microbial metabolism via oxidation or reduction of their (hydro)quinone moieties. As such, they are known to be important electron sinks for respiratory and fermentative bacteria and electron sources for denitrifying and perchlorate-reducing bacteria. HS also strongly promote abiotic reduction of Fe(III) when irradiated with light. Here, we show that HS-enhanced Fe(III) photoreduction can also drive chemolithotrophic microbial respiration by producing Fe(II), which functions as a respiratory electron donor. Due to their molecular complexity, HS absorb most of the electromagnetic spectrum and can act as broad-spectrum antennae converting radiant energy into bioavailable chemical energy. The finding that chemolithotrophic organisms can utilize this energy has important implications for terrestrial, and possibly extraterrestrial, microbial processes and offers an alternative mechanism of radiation-driven primary productivity to that of phototrophy.
腐殖质（HS）是一种高分子量的复杂难降解有机物，广泛存在于陆地和水生环境中。尽管这些化合物难以被微生物降解，但它们仍然可以通过（水）醌部分的氧化或还原来支持微生物代谢。因此，腐殖质被认为是呼吸和发酵细菌的重要电子汇，也是反硝化和高氯酸盐还原细菌的电子源。当受到光照时，腐殖质还强烈促进了铁（III）的非生物还原。在这里，我们表明 HS 增强的 Fe(III)光还原也可以通过产生 Fe(II)来驱动化能自养微生物呼吸，Fe(II)作为呼吸电子供体。由于其分子复杂性，腐殖质吸收了大部分电磁光谱，并且可以作为广谱天线将辐射能转化为生物可用的化学能。化能自养生物可以利用这种能量的发现对陆地，甚至可能是外星，微生物过程具有重要意义，并为辐射驱动的初级生产力提供了一种替代光合作用的机制。
