Smith Jason M, Green Stefan J, Kelley Cheryl A, Prufert-Bebout Leslie, Bebout Brad M
Exobiology Branch, NASA Ames Research Center, Moffett Field, CA, USA.
Environ Microbiol. 2008 Feb;10(2):386-94. doi: 10.1111/j.1462-2920.2007.01459.x. Epub 2007 Dec 19.
Methanogenesis was characterized in hypersaline microbial mats from Guerrero Negro, Baja California Sur, Mexico both in situ and after long-term manipulation in a greenhouse environment. Substrate addition experiments indicate methanogenesis to occur primarily through the catabolic demethylation of non-competitive substrates, under field conditions. However, evidence for the coexistence of other metabolic guilds of methanogens was obtained during a previous manipulation of sulfate concentrations. To fully characterize methanogenesis in these mats, in the absence of competition for reducing equivalents with sulfate-reducing microorganisms, we maintained microbial mats for longer than 1 year under conditions of lowered sulfate and salinity levels. The goal of this study was to assess whether observed differences in methane production during sulfate and salinity manipulation were accompanied by shifts in the composition of methanogen communities. Culture-independent techniques targeting methyl coenzyme M reductase genes (mcrA) were used to assess the dynamics of methanogen assemblages. Clone libraries from mats sampled in situ or maintained at field-like conditions in the greenhouse were exclusively composed of sequences related to methylotrophic members of the Methanosarcinales. Increases in pore water methane concentrations under conditions of low sulfate correlated with an observed increase in the abundance of putatively hydrogenotrophic mcrA, related to Methanomicrobiales. Geochemical and molecular data provide evidence of a significant shift in the metabolic pathway of methanogenesis from a methylotroph-dominated system in high-sulfate environments to a mixed community of methylotrophic and hydrogenotrophic methanogens under low sulfate conditions.
对墨西哥南下加利福尼亚州格雷罗内格罗的高盐度微生物垫中的产甲烷作用进行了原位表征，并在温室环境中进行长期处理后进行了表征。底物添加实验表明，在野外条件下，产甲烷作用主要通过非竞争性底物的分解代谢去甲基化发生。然而，在先前对硫酸盐浓度的处理过程中，获得了其他产甲烷菌代谢群落共存的证据。为了在不存在与硫酸盐还原微生物竞争还原当量的情况下全面表征这些微生物垫中的产甲烷作用，我们在降低硫酸盐和盐度水平的条件下将微生物垫维持了1年以上。本研究的目的是评估在硫酸盐和盐度处理过程中观察到的甲烷产生差异是否伴随着产甲烷菌群落组成的变化。使用针对甲基辅酶M还原酶基因（mcrA）的非培养技术来评估产甲烷菌组合的动态。来自原位采样或在温室中类似野外条件下维持的微生物垫的克隆文库仅由与甲烷八叠球菌甲基营养成员相关的序列组成。在低硫酸盐条件下孔隙水甲烷浓度的增加与观察到的与甲烷微菌目相关的推定氢营养型mcrA丰度的增加相关。地球化学和分子数据提供了证据，表明产甲烷代谢途径发生了重大转变，从高硫酸盐环境中以甲基营养菌为主的系统转变为低硫酸盐条件下甲基营养型和氢营养型产甲烷菌的混合群落。
