Metabolic interactions in methanogenic and sulfate-reducing bioreactors

Abstract

In environments where the amount of electron acceptors is insufficient for complete breakdown of organic matter, methane is formed as the major reduced end product. In such methanogenic environments organic acids are degraded by syntrophic consortia of acetogenic bacteria and methanogenic archaea. Hydrogen consumption by methanogens is essential for acetogenic bacteria to convert organic acids to acetate and hydrogen. Several syntrophic cocultures growing on propionate and butyrate have been described. These syntrophic fatty acid-degrading consortia are affected by the presence of sulfate. When sulfate is present sulfate-reducing bacteria compete with methanogenic archaea for hydrogen and acetate, and with acetogenic bacteria for propionate and butyrate. Sulfate-reducing bacteria easily outcompete methanogens for hydrogen, but the presence of acetate as carbon source may influence the outcome of the competition. By contrast, acetoclastic methanogens can compete reasonably well with acetate-degrading sulfate reducers. Sulfate-reducing bacteria grow much faster on propionate and butyrate than syntrophic consortia.

Carbon dioxide reduction by mixed and pure cultures in microbial electrosynthesis using an assembly of graphite felt and stainless steel as a cathode

“…Though acetate was repetitively produced and consumed, no substantial amounts of alcohols or other higher VFAs were found in the electrolyte. Possible explanation could be the conversion of acetate to CH 4 by acetoclastic methanogens or oxidized by sulfate reducers which are normally present in culture from wastewaters (Stams et al, 2005). Methane was detected up to 10% (v/v) in a number of headspace gas analysis during Batch 1 even though the system was not completely gas tight and irregularly flushed with N 2 .…”

The Electron Transfer System of Syntrophically Grown Desulfovibrio vulgaris

“…The sharing of available energy within communities is particularly important in anaerobic systems, where limited energy is divided among highly specialized and metabolically interdependent populations (36,37,39). In the absence of exogenous electron acceptors such as sulfate and nitrate, the mineralization of organic matter in anoxic environments yields primarily carbon dioxide and methane, and this process is controlled by the synergistic activities of multiple anaerobic microbial populations.…”

Effect of Anaerobic Azo Dye Reduction on Continuous Sludge Digestion

“…SRB was also reported to reduce the sulfonated aromatic compounds other than sulfate those were formed during dye reduction [23]. Since the growth yield of SRB on H 2 may be higher than hydrogenotrophic methanogens [24], the higher growth of SRB may be expected in CR3 resulted for higher VS and TCOD concentrations in the reactor for that period. There would not be any decrease in CH 4 production due to H 2 competition, if the contribution of hydrogenotrophic methanogens to methanogenesis was already low.…”