Fernández-Remolar David C, Gómez Felipe, Prieto-Ballesteros Olga, Schelble Rachel T, Rodríguez Nuria, Amils Ricardo
Centro de Astrobiología, CSIC-INTA, Torrejón de Ardoz, Spain.
Astrobiology. 2008 Feb;8(1):157-73. doi: 10.1089/ast.2006.0022.
Chemolithotrophic communities that colonize subsurface habitats have great relevance for the astrobiological exploration of our Solar System. We hypothesize that the chemical and thermal stabilization of an environment through microbial activity could make a given planetary region habitable. The MARTE project ground-truth drilling campaigns that sampled cryptic subsurface microbial communities in the basement of the Río Tinto headwaters have shown that acidic surficial habitats are the result of the microbial oxidation of pyritic ores. The oxidation process is exothermic and releases heat under both aerobic and anaerobic conditions. These microbial communities can maintain the subsurface habitat temperature through storage heat if the subsurface temperature does not exceed their maximum growth temperature. In the acidic solutions of the Río Tinto, ferric iron acts as an effective buffer for controlling water pH. Under anaerobic conditions, ferric iron is the oxidant used by microbes to decompose pyrite through the production of sulfate, ferrous iron, and protons. The integration between the physical and chemical processes mediated by microorganisms with those driven by the local geology and hydrology have led us to hypothesize that thermal and chemical regulation mechanisms exist in this environment and that these homeostatic mechanisms could play an essential role in creating habitable areas for other types of microorganisms. Therefore, searching for the physicochemical expression of extinct and extant homeostatic mechanisms through physical and chemical anomalies in the Mars crust (i.e., local thermal gradient or high concentration of unusual products such as ferric sulfates precipitated out from acidic solutions produced by hypothetical microbial communities) could be a first step in the search for biological traces of a putative extant or extinct Mars biosphere.
定殖于地下生境的化能无机营养群落对于太阳系的天体生物学探索具有重大意义。我们推测，通过微生物活动实现的环境化学和热稳定作用可能使特定的行星区域适宜居住。“火星参考任务”（MARTE）项目的实地钻探活动对力拓河源头基底中隐秘的地下微生物群落进行了采样，结果表明，酸性地表生境是黄铁矿矿石微生物氧化的结果。氧化过程是放热的，在有氧和无氧条件下都会释放热量。如果地下温度不超过其最高生长温度，这些微生物群落可以通过储存热量来维持地下生境的温度。在力拓河的酸性溶液中，三价铁作为控制水体pH值的有效缓冲剂。在厌氧条件下，三价铁是微生物用于通过产生硫酸盐、二价铁和质子来分解黄铁矿的氧化剂。微生物介导的物理和化学过程与由当地地质和水文驱动的过程之间的整合，使我们推测在这种环境中存在热调节和化学调节机制，并且这些稳态机制可能在为其他类型的微生物创造宜居区域方面发挥重要作用。因此，通过火星地壳中的物理和化学异常（即局部热梯度或异常产物的高浓度，如假设的微生物群落产生的酸性溶液中沉淀出的硫酸铁）来寻找已灭绝和现存稳态机制的物理化学表现，可能是寻找假定的现存或已灭绝的火星生物圈生物痕迹的第一步。
