The aim of this research was to investigate the competition between methanogens and sulfate-reducing bacteria in hypersaline environments. Samples of photosynthetic microbial mats, both soft mats (salinities of 55–126 ppt) and gypsum-hosted endoevaporite mats (salinities of 77–320 ppt), were obtained from hypersaline environments in California, USA, Mexico and Chile. Methane production was determined from the increase in headspace methane concentration within incubation vials containing mat samples. At the end of the incubation period, the δ¹³C values of produced methane were measured. Soft microbial mat vials containing molybdate, a specific inhibitor of bacterial sulfate reduction, exhibited dramatically higher methane production rates and higher (enriched in ¹³C) methane δ¹³C values than the controls. This suggests that the inhibition of sulfate reduction allowed the methanogens at these sites to use the competitive substrates (H₂ and/or acetate) made available. Further, the higher δ¹³C values of the produced methane suggest that substrates (both competitive and non-competitive) were used to near completion. At the endoevaporite sites, which have much higher salinities than the soft mat sites, methane production was not significantly different and the methane δ¹³C values either remained the same or decreased (depleted in ¹³C) with added molybdate. We suggest that substrate availability increased enough to allow for somewhat greater isotopic fractionation resulting in the lower methane δ¹³C values that were observed, but not enough to significantly increase measured production rates. Where no changes in either methane production rates or δ¹³C values occurred, we hypothesize that salinity itself was inhibiting sulfate reduction and thus controlling microbe populations and rates of metabolism.

中文翻译：

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高盐环境下细菌硫酸盐还原抑制作用对甲烷产生和稳定同位素组成的影响

这项研究的目的是研究高盐环境中产甲烷菌与减少硫酸盐的细菌之间的竞争。从加利福尼亚，美国，墨西哥和智利的高盐环境中获得了光合微生物垫的样品，包括软垫（盐度为55-126 ppt）和石膏基内挥发物垫（盐度为77-320 ppt）。甲烷的产生是通过含有垫子样品的培养瓶中顶空甲烷浓度的增加来确定的。在温育期结束时，该δ ¹³测定产生的甲烷的C值。含有钼酸盐（一种抑制细菌硫酸盐还原的特效剂）的柔软微生物瓶，显示出更高的甲烷产生速率和更高的（富含¹³ C）甲烷δ¹³下比对照值。这表明对硫酸盐还原的抑制使这些位点的产甲烷菌能够使用可获得的竞争性底物（H ₂和/或乙酸盐）。此外，较高的δ ¹³的C值产生的甲烷表明，底物（无论是竞争性和非竞争性）被用来接近完成。在endoevaporite位点，其具有比软垫位点高得多的盐度，甲烷产量为不显著不同，甲烷δ ^13个C值或者保持不变或者下降（贫¹³ C）用加入钼酸盐。我们建议底物的利用率增加到足以允许更大的同位素分馏，从而导致较低的甲烷δ观察到¹³ C值，但不足以显着提高测得的生产率。其中在任一甲烷生产速率或δ无变化^13个C值发生，我们假设盐度本身抑制硫酸盐还原并因此控制微生物种群和代谢率。