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Methanogens and Methanogenesis in Hypersaline Environments


Methanogenesis in hypersaline environments is determined by redox potential and permanency of anaerobic conditions, and by the concentration of other terminal electron acceptors, particularly sulfate, because sulfate-reducing bacteria have a greater affinity than methanogens for competitive substrates like hydrogen and acetate. Hypersalinity, however, is not an obstacle to methanogenesis; in many cases it provides higher concentrations of non-competitive substrates like methylamines, which derive from compatible solutes such as glycine-betaine that is synthesized by many microbes inhabiting hypersaline environments. Also, depletion of sulfate, as may occur in deeper sediments, allows increased methanogenesis. On the other hand, increasing salinity requires methanogens to synthesize or take up more compatible solutes at a significant energetic cost. Aceticlastic and hydrogenotrophic methanogens, with their lower energetic