Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University, Frankfurt am Main, Germany.
ISME J. 2020 Jun;14(6):1561-1570. doi: 10.1038/s41396-020-0627-1. Epub 2020 Mar 16.
Interspecies hydrogen transfer in anoxic ecosystems is essential for the complete microbial breakdown of organic matter to methane. Acetogenic bacteria are key players in anaerobic food webs and have been considered as prime candidates for hydrogen cycling. We have tested this hypothesis by mutational analysis of the hydrogenase in the model acetogen Acetobacterium woodii. Hydrogenase-deletion mutants no longer grew on H + CO or organic substrates such as fructose, lactate, or ethanol. Heterotrophic growth could be restored by addition of molecular hydrogen to the culture, indicating that hydrogen is an intermediate in heterotrophic growth. Indeed, hydrogen production from fructose was detected in a stirred-tank reactor. The mutant grew well on organic substrates plus caffeate, an alternative electron acceptor that does not require molecular hydrogen but NADH as reductant. These data are consistent with the notion that molecular hydrogen is produced from organic substrates and then used as reductant for CO reduction. Surprisingly, hydrogen cycling in A. woodii is different from the known modes of interspecies or intraspecies hydrogen cycling. Our data are consistent with a novel type of hydrogen cycling that connects an oxidative and reductive metabolic module in one bacterial cell, "intracellular syntrophy."
在缺氧生态系统中，种间氢转移对于将有机物完全分解为甲烷是必不可少的。乙酰生成菌是厌氧食物网中的关键参与者，并且被认为是氢循环的主要候选者。我们通过对模型产乙酸菌乙酰乙酸木聚糖的氢化酶进行突变分析来验证这一假设。氢化酶缺失突变体不再在 H ⁇ + CO 或果糖、乳酸盐或乙醇等有机底物上生长。在培养物中添加氢气可以恢复异养生长，表明氢气是异养生长的中间产物。事实上，在搅拌罐反应器中检测到从果糖中产生氢气。该突变体在有机底物加咖啡酸上生长良好，咖啡酸是一种替代电子受体，不需要氢气，但需要 NADH 作为还原剂。这些数据与以下观点一致，即氢气是从有机底物中产生的，然后用作 CO 还原的还原剂。令人惊讶的是，A. woodii 中的氢循环与已知的种间或种内氢循环模式不同。我们的数据与一种新型的氢循环一致，该循环将一个细菌细胞中的氧化和还原代谢模块连接起来，称为“细胞内共生”。
