Department of Plant and Microbial Biology, University of Minnesota, Twin Cities, St. Paul, Minnesota, USA.
Appl Environ Microbiol. 2022 Dec 13;88(23):e0115922. doi: 10.1128/aem.01159-22. Epub 2022 Nov 14.
The complete remineralization of organic matter in anoxic environments relies on communities of microorganisms that ferment organic acids and alcohols to CH. This is accomplished through syntrophic association of H or formate producing bacteria and methanogenic archaea, where exchange of these intermediates enables growth of both organisms. While these communities are essential to Earth's carbon cycle, our understanding of the dynamics of H or formate exchanged is limited. Here, we establish a model partnership between Syntrophotalea carbinolica and Methanococcus maripaludis. Through sequencing a transposon mutant library of M. maripaludis grown with ethanol oxidizing S. carbinolica, we found that genes encoding the F-dependent formate dehydrogenase (Fdh) and F-dependent methylene-tetrahydromethanopterin dehydrogenase (Mtd) are important for growth. Competitive growth of M. maripaludis mutants defective in either H or formate metabolism verified that, across multiple substrates, interspecies formate exchange was dominant in these communities. Agitation of these cultures to facilitate diffusive loss of H to the culture headspace resulted in an even greater competitive advantage for M. maripaludis strains capable of oxidizing formate. Finally, we verified that an M. maripaludis mutant had a defect during syntrophic growth. Together, these results highlight the importance of formate exchange for the growth of methanogens under syntrophic conditions. In the environment, methane is typically generated by fermentative bacteria and methanogenic archaea working together in a process called syntrophy. Efficient exchange of small molecules like H or formate is essential for growth of both organisms. However, difficulties in determining the relative contribution of these intermediates to methanogenesis often hamper efforts to understand syntrophic interactions. Here, we establish a model syntrophic coculture composed of S. carbinolica and the genetically tractable methanogen M. maripaludis. Using mutant strains of M. maripaludis that are defective for either H or formate metabolism, we determined that interspecies formate exchange drives syntrophic growth of these organisms. Together, these results advance our understanding of the degradation of organic matter in anoxic environments.
在缺氧环境中，有机物的完全矿化依赖于能够发酵有机酸和醇类生成 CH 的微生物群落。这是通过产 H 或甲酸盐的细菌和产甲烷古菌的共营养关联来实现的，其中这些中间产物的交换使两种生物体都能够生长。虽然这些群落对地球的碳循环至关重要，但我们对 H 或甲酸盐交换动态的理解是有限的。在这里，我们建立了 Syntrophotalea carbinolica 和 Methanococcus maripaludis 之间的模型伙伴关系。通过对在乙醇氧化的 S. carbinolica 生长过程中进行转座子突变的 M. maripaludis 文库进行测序，我们发现编码 F 依赖型甲酸盐脱氢酶 (Fdh) 和 F 依赖型亚甲基四氢叶酸脱氢酶 (Mtd) 的基因对生长很重要。在多种底物中，M. maripaludis 突变体的竞争生长证实，在这些群落中，种间甲酸盐交换是主要的。搅动这些培养物以促进 H 扩散到培养物的气相中，使得能够氧化甲酸盐的 M. maripaludis 菌株具有更大的竞争优势。最后，我们验证了 M. maripaludis 突变体在共营养生长过程中存在缺陷。总之，这些结果强调了在共营养条件下甲酸盐交换对产甲烷菌生长的重要性。在环境中，甲烷通常是由发酵细菌和产甲烷古菌共同作用产生的，这一过程称为共营养作用。小分子如 H 或甲酸盐的有效交换对两种生物体的生长都是必不可少的。然而，确定这些中间产物对甲烷生成的相对贡献的困难往往阻碍了对共营养相互作用的理解。在这里，我们建立了由 S. carbinolica 和遗传上易于操作的产甲烷菌 M. maripaludis 组成的模型共培养物。使用 M. maripaludis 的突变株，这些突变株在 H 或甲酸盐代谢方面存在缺陷，我们确定种间甲酸盐交换驱动了这些生物体的共营养生长。总之，这些结果提高了我们对缺氧环境中有机物降解的理解。
