Methanogenic archaea and sulfate reducing bacteria co-cultured on acetate: teamwork or coexistence?

Abstract

Acetate is a major product of fermentation processes and an important substrate for sulfate reducing bacteria and methanogenic archaea. Most studies on acetate catabolism by sulfate reducers and methanogens have used pure cultures. Less is known about acetate conversion by mixed pure cultures and the interactions between both groups. We tested interspecies hydrogen transfer and coexistence between marine methanogens and sulfate reducers using mixed pure cultures of two types of microorganisms. First, Desulfovibrio vulgaris subsp. vulgaris (DSM 1744), a hydrogenotrophic sulfate reducer, was cocultured together with the obligate aceticlastic methanogen Methanosaeta concilii using acetate as carbon and energy source. Next, Methanococcus maripaludis S2, an obligate H2- and formate-utilizing methanogen, was used as a partner organism to M. concilii in the presence of acetate. Finally, we performed a coexistence experiment between M. concilii and an acetotrophic sulfate reducer Desulfobacter latus AcSR2. Our results showed that D. vulgaris was able to reduce sulfate and grow from hydrogen leaked by M. concilii. In the other coculture, M. maripaludis was sustained by hydrogen leaked by M. concilii as revealed by qPCR. The growth of the two aceticlastic microbes indicated co-existence rather than competition. Altogether, our results indicate that H2 leaking from M. concilii could be used by efficient H2-scavengers. This metabolic trait, revealed from coculture studies, brings new insight to the metabolic flexibility of methanogens and sulfate reducers residing in marine environments in response to changing environmental conditions and community compositions. Using dedicated physiological studies we were able to unravel the occurrence of less obvious interactions between marine methanogens and sulfate-reducing bacteria.

Genetic, Genomic, and Transcriptomic Studies of Pyruvate Metabolism in Methanosarcina barkeri Fusaro

“…It is possible that the population of Pyr ϩ cells in the aggregates is not biochemically homogeneous, with one subset of the population performing hydrogenotrophic methanogenesis and the second aceticlastic methanogenesis. It has been reported that these two reactions can be coordinated between two methanogenic strains (30). Since H 2 inhibits aceticlastic growth, in the cell aggregates, hydrogenotrophic methanogens would lower the H 2 partial pressure to a level that would allow aceticlastic methanogenesis to occur and therefore allow the organism to metabolize pyruvate.…”

Evaluating the microbial community and gene regulation involved in crystallization kinetics of ZnS formation in reduced environments

“…A similar study observed Desulfovibrio and Desulfomicrobium persisting in ethanol fed pilot-scale bioreactors, yet low levels of methanogens . These studies, as well 71 as others Ozuolmez et al, 2015;Paulo et al, 2015) highlight two important interactions in anaerobic settings; SRB competition with methanogenic archaea for substrates, and SRB reliance on the degradation production of fermentive acetogens. Both scenarios contribute to successful passive treatment systems for ARD, as they influence the livelihood of the primary metal-immobilizing agents, sulfate reducing bacteria.…”

“…However, rarely in nature do individual microbial groups function alone; rather there exists a complex network of substrate sharing and/or competition between different bacterial guilds, often partitioned by distinct chemical or redox zones. SRB will coexist with multiple species, contending for carbon substrates with methanogens and homoacetogens, and often relying on the degradation products of amino acids, sugars, and long-chain fatty acids by fermentative bacteria Ozuolmez et al, 2015). Few studies have explored the interactions of SRB with other species and associated metalsulfide precipitation (Alexandrino et al, 2014;Zhang et al, 2016), thus a research gap exists in this context.…”

Archaea in Natural and Impacted Brazilian Environments

“…However, a cooccurrence of sulfate reducing bacteria and methanogens was detected, indicating either that the abundance of organic matter allows the presence of these organisms by reducing substrate competition or that the detected methanogens are capable of using substrates that are not used by sulfate reducing bacteria. A recent article described the dynamics of hydrogen transfer between an acetoclastic methanogen and hydrogenotrophic microorganisms, grown in pure and mixed cultures, and the results suggest that these organisms coexist and do not compete in marine sediments [62]. …”