Enrichment and isolation of acidophilic sulfate‐reducing bacteria from T into R iver sediments

Summary Although some acidophilic and alkaliphilic species have been described recently, most of the known sulfate‐reducing bacteria ( SRB ) grow optimally at neutral pH. In this study, sulfate reduction was studied with sediment samples from the extremely acidic T into R iver basin. Stable enrichments of SRB were obtained at pH 4 with glycerol, methanol and hydrogen; at pH 4.5 with lactate and at pH 5.5 with succinate as substrates. Inhibition of sulfate reduction by organic acids below their p K a was observed. Cloning and sequencing of 16 S r RNA gene showed that fermentative bacteria ( P aludibacter spp., O scillibacter spp.) and SRB ( T hermodesulfobium spp., D esulfosporosinus spp., D esulfitobacterium spp., D esulfotomaculum spp.) were co‐enriched. By repeated serial dilutions and streaking on agar plates, four strains of SRB belonging to the F irmicutes phylum were obtained. Two of them show 96% 16 S r RNA gene sequence similarity with D esulfosporosinus acidophilus, and a third one with D esulfosporosinus orientis . Another isolate has just 93% r RNA gene sequence similarity with the D esulfosporosinus/ D esulfitobacterium cluster and might represent a novel species within a novel genus. One of the D esulfosporosinus strains was further investigated showing maximum growth at pH 5.5, and a pH ‐dependent inhibitory effect of organic acids and sulfide.