Coon Gage R, Duesing Paul D, Paul Raegan, Baily Jennifer A, Lloyd Karen G
Department of Microbiology, The University of Tennessee, Knoxville, TN, United States.
Front Microbiol. 2023 Oct 6;14:1268361. doi: 10.3389/fmicb.2023.1268361. eCollection 2023.
Anaerobic oxidation of methane (AOM) is hypothesized to occur through reverse hydrogenotrophic methanogenesis in marine sediments because sulfate reducers pull hydrogen concentrations so low that reverse hydrogenotrophic methanogenesis is exergonic. If true, hydrogenotrophic methanogenesis can theoretically co-occur with sulfate reduction if the organic matter is so labile that fermenters produce more hydrogen than sulfate reducers can consume, causing hydrogen concentrations to rise. Finding accumulation of biologically-produced methane in sulfate-containing organic-rich sediments would therefore support the theory that AOM occurs through reverse hydrogenotrophic methanogenesis since it would signal the absence of net AOM in the presence of sulfate.
16S rRNA gene libraries were compared to geochemistry and incubations in high depth-resolution sediment cores collected from organic-rich Cape Lookout Bight, North Carolina.
We found that methane began to accumulate while sulfate is still abundant (6-8 mM). Methane-cycling archaea , , and also increased at these depths. Incubations showed that methane production in the upper 16 cm in sulfate-rich sediments was biotic since it could be inhibited by 2-bromoethanosulfonoic acid (BES).
We conclude that methanogens mediate biological methane production in these organic-rich sediments at sulfate concentrations that inhibit methanogenesis in sediments with less labile organic matter, and that methane accumulation and growth of methanogens can occur under these conditions as well. Our data supports the theory that H concentrations, rather than the co-occurrence of sulfate and methane, control whether methanogenesis or AOM via reverse hydrogenotrophic methanogenesis occurs. We hypothesize that the high amount of labile organic matter at this site prevents AOM, allowing methane accumulation when sulfate is low but still present in mM concentrations.
甲烷厌氧氧化（AOM）被认为是通过海洋沉积物中的逆向氢营养型产甲烷作用发生的，因为硫酸盐还原菌会将氢气浓度拉低至逆向氢营养型产甲烷作用为放能反应的水平。如果这一假设成立，那么理论上如果有机物非常不稳定，以至于发酵菌产生的氢气量超过硫酸盐还原菌的消耗量，导致氢气浓度上升，氢营养型产甲烷作用就可以与硫酸盐还原同时发生。因此，在富含硫酸盐的富含有机物的沉积物中发现生物产生的甲烷的积累将支持AOM通过逆向氢营养型产甲烷作用发生的理论，因为这将表明在有硫酸盐存在的情况下不存在净AOM。
将16S rRNA基因文库与从北卡罗来纳州富含有机物的瞭望角湾采集的高深度分辨率沉积物岩心中的地球化学数据和培养实验结果进行比较。
我们发现，在硫酸盐仍然丰富（6 - 8 mM）时甲烷就开始积累。在这些深度，参与甲烷循环的古菌、 和 也有所增加。培养实验表明，富含硫酸盐的沉积物上部16厘米处的甲烷产生是生物作用，因为它可以被2 - 溴乙烷磺酸钠（BES）抑制。
我们得出结论，在这些富含有机物的沉积物中，产甲烷菌在抑制较难分解有机物的沉积物中产甲烷作用的硫酸盐浓度下介导生物甲烷的产生，并且在这些条件下也会发生甲烷积累和产甲烷菌的生长。我们的数据支持这样一种理论，即氢气浓度而非硫酸盐和甲烷的共存控制着是发生产甲烷作用还是通过逆向氢营养型产甲烷作用进行AOM。我们推测，该地点大量的不稳定有机物阻止了AOM的发生，使得在硫酸盐浓度较低但仍处于毫摩尔浓度时甲烷得以积累。
