Metabolism of novel potential syntrophic acetate-oxidizing bacteria in thermophilic methanogenic chemostats

Abstract

Acetate is a major intermediate in the anaerobic digestion of organic waste to produce CH 4 . In methanogenic systems, acetate degradation is carried out by either acetoclastic methanogenesis or syntrophic degradation by acetate oxidizers and hydrogenotrophic methanogens. Due to challenges in the isolation of syntrophic acetate-oxidizing bacteria (SAOB), the diversity and metabolism of SAOB and the mechanisms of their interactions with methanogenic partners are not fully characterized. In this study, the in situ activity and metabolic characteristics of potential SAOB and their interactions with methanogens were elucidated through metagenomics and metatranscriptomics. In addition to the reported SAOB classified in the genera Tepidanaerobacter , Desulfotomaculum , and Thermodesulfovibrio , we identified a number of potential SAOB that are affiliated with Clostridia , Thermoanaerobacteraceae, Anaerolineae, and Gemmatimonadetes. The potential SAOB possessing the glycine-mediated acetate oxidation pathway dominates SAOB communities. Moreover, formate appeared to be the main product of the acetate degradation by the most active potential SAOB. We identified the methanogen partner of these potential SAOB in the acetate-fed chemostat as Methanosarcina thermophila . The dominated potential SAOB in each chemostat had similar metabolic characteristics, even though they were in different fatty-acid-fed chemostats. These novel syntrophic lineages are prevalent and may play critical roles in thermophilic methanogenic reactors. This study expands our understanding of the phylogenetic diversity and in situ biological functions of uncultured syntrophic acetate degraders and presents novel insights into how they interact with methanogens. IMPORTANCE Combining reactor operation with omics provides insights into novel uncultured syntrophic acetate degraders and how they perform in thermophilic anaerobic digesters. This improves our understanding of syntrophic acetate degradation and contributes to the background knowledge necessary to better control and optimize anaerobic digestion processes.

High synthetic cost-amino acids reduce member interactions of acetate-degrading methanogenic microbial community

“…Most of members in the community were AA auxotrophs and formed AA exchange interactions with each other ( Yao et al, 2021 ). In addition to this, there are large differences in energy acquisition among these members ( Zeng et al, 2024 ), while avoiding overlapping ecological niches. Thus, in our results, changes in AA accessibility in the environment had a more pronounced effect on bacterial genera with low energy accessibility and did not lead to the collapse of the microbial community.…”

“…Seed sludge taken from a stably operating thermophilic methanogenic chemostat fed with acetate as the sole carbon source ( Zeng et al, 2024 ) was used to inoculate five completely mixed continuous thermophilic methanogenic reactors with a working volume of 400 ml. The reactors were fed with synthetic wastewater [total organic carbon (TOC): 8 g/L] with acetate as the sole carbon source.…”

“…The reactors were fed with synthetic wastewater [total organic carbon (TOC): 8 g/L] with acetate as the sole carbon source. Detailed concentrations of inorganic salt fractions, trace elements, and vitamins in the synthetic wastewater can be found in the study by Yao et al (2021) and Zeng et al (2024) . The reactors were operated at a dilution rate of 0.1 d −1 with a hydraulic retention time (HRT) of 10 days at 55°C.…”