Kujala Katharina, Schmidt Oliver, Horn Marcus A
Water, Energy and Environmental Engineering Research Unit, University of Oulu, Oulu, Finland.
Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway.
Front Microbiol. 2024 Dec 11;15:1428517. doi: 10.3389/fmicb.2024.1428517. eCollection 2024.
Peatlands are invaluable but threatened ecosystems that store huge amounts of organic carbon globally and emit the greenhouse gasses carbon dioxide (CO) and methane (CH). Trophic interactions of microbial groups essential for methanogenesis are poorly understood in such systems, despite their importance. Thus, the present study aimed at unraveling trophic interactions between fermenters and methanogens in a nitrogen-limited, subarctic, pH-neutral fen. CH emission measurements indicated that the fen is a source of CH, and that CH emissions were higher in plots supplemented with ammonium compared to unsupplemented plots. The amino sugar N-acetylglucosamine was chosen as model substrate for peat fermenters since it can serve as organic carbon and nitrogen source and is a monomer of chitin and peptidoglycan, two abundant biopolymers in the fen. Supplemental N-acetylglucosamine was fermented to acetate, ethanol, formate, and CO during the initial incubation of anoxic peat soil microcosms without preincubation. Subsequently, ethanol and formate were converted to acetate and CH. When methanogenesis was inhibited by bromoethanesulfonate, acetate and propionate accumulated. Long-term preincubation considerably increased CH production in unsupplemented microcosms and microcosms supplemented with methanogenic substrates. Supplemental H-CO and formate stimulated methanogenesis the most, whereas acetate had an intermediary and methanol a minor stimulatory effect on methane production in preincubated microcosms. Activity of acetogens was suggested by net acetate production in microcosms supplemented with H-CO, formate, and methanol. Microbial community analysis of field fresh soil indicated the presence of many physiologically unresolved bacterial taxa, but also known primary and secondary fermenters, acetogens, iron reducers, sulfate reducers, and hydrogenotrophic methanogens (predominately and ). Aceticlastic methanogens were either not abundant () or could not be detected due to limited coverage of the used primers (). The collective results indicate a complex interplay of synergy and competition between fermenters, methanogens, acetogens, and potentially iron as well as sulfate reducers. While acetate derived from fermentation or acetogenesis in this pH-neutral fen likely plays a crucial role as carbon source for the predominant hydrogenotrophic methanogens, it remains to be resolved whether acetate is also converted to CH via aceticlastic methanogenesis and/or syntrophic acetate oxidation coupled to hydrogenotrophic methanogenesis.
泥炭地是全球储存大量有机碳并排放温室气体二氧化碳（CO）和甲烷（CH）的重要但受到威胁的生态系统。尽管这些系统中对于产甲烷至关重要的微生物群落的营养相互作用很重要，但人们对此了解甚少。因此，本研究旨在揭示在氮限制、亚北极、pH 中性的泥炭沼泽中发酵菌和产甲烷菌之间的营养相互作用。CH排放测量表明，该泥炭沼泽是CH的一个排放源，并且与未添加铵的地块相比，添加铵的地块中CH排放量更高。氨基糖N - 乙酰葡糖胺被选作泥炭发酵菌的模型底物，因为它可以作为有机碳和氮源，并且是几丁质和肽聚糖的单体，这两种是泥炭沼泽中丰富的生物聚合物。在没有预培养的缺氧泥炭土微观模型的初始培养过程中，补充的N - 乙酰葡糖胺被发酵成乙酸、乙醇、甲酸和CO。随后，乙醇和甲酸被转化为乙酸和CH。当产甲烷作用被溴乙烷磺酸盐抑制时，乙酸和丙酸积累。长期预培养显著增加了未补充底物的微观模型和补充了产甲烷底物的微观模型中的CH产量。补充的H - CO和甲酸对产甲烷作用的刺激最大，而乙酸在预培养的微观模型中对甲烷产生有中等刺激作用，甲醇有较小的刺激作用。在补充了H - CO、甲酸和甲醇的微观模型中净乙酸产生表明了产乙酸菌的活性。对田间新鲜土壤的微生物群落分析表明存在许多生理功能未明确的细菌分类群，但也有已知的初级和次级发酵菌、产乙酸菌、铁还原菌、硫酸盐还原菌和氢营养型产甲烷菌（主要是 和 ）。乙酸裂解产甲烷菌要么不丰富（ ），要么由于所用引物覆盖范围有限而未被检测到（ ）。总体结果表明发酵菌、产甲烷菌、产乙酸菌以及潜在的铁还原菌和硫酸盐还原菌之间存在协同和竞争的复杂相互作用。虽然在这个pH中性的泥炭沼泽中，由发酵或产乙酸作用产生的乙酸可能作为主要氢营养型产甲烷菌的碳源发挥关键作用，但乙酸是否也通过乙酸裂解产甲烷作用和/或与氢营养型产甲烷作用耦合的互营乙酸氧化转化为CH仍有待解决。
