Phylogenetic and physiological diversity of sulphate-reducing bacteria isolated from a salt marsh sediment

The phylogenetic and physiological diversity of sulphate-reducing bacteria inhabiting a salt marsh rhizosphere were investigated. Sulphate-reducing ba cteria were isolated from a salt marsh rhizosphere using enrichment culture s with electron donors thought to be prevalent in the rhizosphere of Sparti na alterniflora. The relationship between phylogeny and nutritional charact eristics of 10 strains was investigated. None of the isolates had 16S rRNA sequences identical to other delta subclass sulphate-reducers, sharing 85.3 to 98.1% sequence similarity with 16S rRNA sequences of their respective c losest relatives. Phylogenetic analysis placed two isolates, obtained with ethanol as an electron donor, within the Desulfovibrionaceae. Seven isolate s, obtained with acetate, butyrate, propionate, or benzoate, were placed wi thin the Desulfobacteriaceae. One isolate, obtained with butyrate, fell wit hin the Desulfobulbus assemblage, which is currently considered part of the Desulfobacteriaceae family. However, due to the phylogenetic breadth and p hysiological traits of this group, we propose that it be considered a new f amily, the "Desulfobulbusaceae." The isolates utilised an array of electron donors similar to their closest relatives with a few exceptions. As a whol e, the phylogenetic and physiological data indicate isolation of several su lphate-reducing bacteria which might be considered as new species and repre sentative of new genera. Comparison of the Desulfobacteriaceae isolates' 16 S rRNA sequences to environmental clones originating from the same study si te revealed that none shared more than 86% sequence similarity. The results provide further insight into the diversity of sulphate-reducing bacteria i nhabiting the salt marsh ecosystem, as well as supporting general trends in the phylogenetic coherence of physiological traits of delta Proteobacteria sulphate reducers.