Ifremer, Univ Brest, CNRS, Laboratoire de Microbiologie des Environnements Extrêmes, Plouzané, France.
ISME J. 2021 Dec;15(12):3423-3436. doi: 10.1038/s41396-021-01020-x. Epub 2021 Jun 4.
Removal of reducing equivalents is an essential catabolic process for all microorganisms to maintain their internal redox balance. The electron disposal by chemoorganotrophic Thermococcales generates H by proton reduction or HS in presence of S. Although in the absence of S growth of these (hyper)thermopiles was previously described to be H-limited, it remains unclear how Thermococcales could be present in H-rich S-depleted habitats. Here, we report that 12 of the 47 strains tested, distributed among all three orders of Thermococcales, could grow without S at 0.8 mM dissolved H and that tolerance to H was always associated with formate production. Two conserved gene clusters coding for a formate hydrogenlyase (FHL) and a putative formate dehydrogenase-NAD(P)H-oxidoreductase were only present in H-dependent formate producers, and were both systematically associated with a formate dehydrogenase and a formate transporter. As the reaction involved in this alternative pathway for disposal of reducing equivalents was close to thermodynamic equilibrium, it was strongly controlled by the substrates-products concentration ratio even in the presence of S. Moreover, experimental data and thermodynamic modelling also demonstrated that H-dependent CO reduction to formate could occur within a large temperature range in contrasted hydrothermal systems, suggesting it could also provide an adaptive advantage.
去除还原当量是所有微生物维持其内部氧化还原平衡的基本分解代谢过程。化能有机异养的泉古菌通过质子还原或在 S 存在下产生 HS 来处理电子。尽管在没有 S 的情况下，这些（超）热球菌以前被描述为 H 限制生长，但仍不清楚热球菌如何存在于富含 H 且 S 耗尽的栖息地中。在这里，我们报告在 0.8 mM 溶解 H 的条件下，测试的 47 株菌株中的 12 株（分布在泉古菌的所有三个目）可以在没有 S 的情况下生长，并且对 H 的耐受性总是与甲酸盐的产生有关。两个保守的基因簇编码甲酸氢酶 (FHL) 和一种假定的甲酸脱氢酶-NAD(P)H-氧化还原酶，仅存在于依赖 H 的甲酸产生菌中，并且都与甲酸脱氢酶和甲酸转运蛋白系统相关。由于该替代途径中用于处理还原当量的反应接近热力学平衡，因此即使存在 S，它也强烈受到底物-产物浓度比的控制。此外，实验数据和热力学模型还表明，依赖 H 的 CO 还原为甲酸可以在较大的温度范围内在对比鲜明的热液系统中发生，这表明它也可以提供适应优势。
