LAUSR

Cultivation and molecular approaches were used to study methanogenesis in saline aquatic system of the Lake Elton (southern Russia), the largest hypersaline lake in Europe. The potential rates of hydrogenotrophic, acetoclastic, methylotrophic and methyl-reducing methanogenesis and diversity of the growth-enriched for by adding electron donors methanogenic communities were studied in the sediment slurry incubations at salinity range from 7 to 275 g/L. The most active pathway detected at all salinities was methylotrophic with a dominance of Methanohalobium and Methanohalophilus genera, at salt saturation and moderately halophilic Methanolobus and Methanococcoides at lower salinity. The absence of methane production from acetate, formate and H 2 /CO 2 under hypersaline conditions was most probably associated with the energy constraints. The contribution of hydrogenotrophic, acetoclastic, and methyl-reducing methanogens to the community increases with a decrease in salinity. Temperature might play an important regulatory function in hypersaline habitats; i.e. methylotrophic methanogens and hydrogenotrophic sulfate-reducing bacteria (SRB) outcompeting methyl-reducing methanogens under mesophilic conditions, and vice versa under thermophilic conditions. An active methane production together with negligible methane oxidation makes hypersaline environments a potential source of methane emission.