Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA.
ISME J. 2012 Apr;6(4):863-74. doi: 10.1038/ismej.2011.142. Epub 2011 Oct 20.
Hydrogen (H(2)) release from photosynthetic microbial mats has contributed to the chemical evolution of Earth and could potentially be a source of renewable H(2) in the future. However, the taxonomy of H(2)-producing microorganisms (hydrogenogens) in these mats has not been previously determined. With combined biogeochemical and molecular studies of microbial mats collected from Elkhorn Slough, Monterey Bay, California, we characterized the mechanisms of H(2) production and identified a dominant hydrogenogen. Net production of H(2) was observed within the upper photosynthetic layer (0-2 mm) of the mats under dark and anoxic conditions. Pyrosequencing of rRNA gene libraries generated from this layer demonstrated the presence of 64 phyla, with Bacteriodetes, Cyanobacteria and Proteobacteria dominating the sequences. Sequencing of rRNA transcripts obtained from this layer demonstrated that Cyanobacteria dominated rRNA transcript pyrotag libraries. An OTU affiliated to Microcoleus spp. was the most abundant OTU in both rRNA gene and transcript libraries. Depriving mats of sunlight resulted in an order of magnitude decrease in subsequent nighttime H(2) production, suggesting that newly fixed carbon is critical to H(2) production. Suppression of nitrogen (N(2))-fixation in the mats did not suppress H(2) production, which indicates that co-metabolic production of H(2) during N(2)-fixation is not an important contributor to H(2) production. Concomitant production of organic acids is consistent with fermentation of recently produced photosynthate as the dominant mode of H(2) production. Analysis of rRNA % transcript:% gene ratios and H(2)-evolving bidirectional [NiFe] hydrogenase % transcript:% gene ratios indicated that Microcoelus spp. are dominant hydrogenogens in the Elkhorn Slough mats.
光合微生物席中氢气（H2）的释放促进了地球的化学演化，并且未来可能成为可再生 H2 的来源。然而，这些席中的产生氢气的微生物（产氢菌）的分类尚未确定。通过对加利福尼亚州蒙特雷湾埃尔克霍恩沼泽采集的微生物席进行生物地球化学和分子联合研究，我们确定了 H2 产生的机制并鉴定出了优势产氢菌。在黑暗和缺氧条件下，席的上层光合层（0-2 毫米）中观察到 H2 的净产生。从该层生成的 rRNA 基因文库的 pyrosequencing 表明，有 64 个门，其中 Bacteriodetes、Cyanobacteria 和 Proteobacteria 占主导地位。从该层获得的 rRNA 转录物的测序表明，Cyanobacteria 主导 rRNA 转录物 pyrotag 文库。与 Microcoleus spp. 相关的 OTU 在 rRNA 基因和转录物文库中均为最丰富的 OTU。剥夺席的阳光导致随后夜间 H2 产生的数量级减少，这表明新固定的碳对 H2 产生至关重要。抑制席中的氮（N2）固定并没有抑制 H2 的产生，这表明 N2 固定过程中的共代谢 H2 产生不是 H2 产生的重要贡献者。有机酸的同时产生与最近产生的光合产物的发酵一致，是 H2 产生的主要模式。rRNA %转录：%基因比值和 H2 进化双向[NiFe]氢化酶%转录：%基因比值的分析表明，Microcoelus spp. 是埃尔克霍恩沼泽席中的优势产氢菌。
