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Abstract

Five psychrophilic, Gram-negative, sulfate-reducing bacteria were isolated from marine sediments off the coast of Svalbard. All isolates grew at the in situ temperature of -1.7 degrees C. In batch cultures, strain PSv29(T) had the highest growth rate at 7 degrees C, strains ASv26(T) and LSv54(T) had the highest growth rate at 10 degrees C, and strains LSV21(T) and LSv514(T) had the highest growth rate at 18 degrees C. The new isolates used the most common fermentation products in marine sediments, such as acetate, propionate, butyrate, lactate and hydrogen, but only strain ASv26(T) was able to oxidize fatty acids completely to CO2. The new strains had growth optima at neutral ph and marine salt concentration, except for LSv54(T) which grew fastest with 1% NaCl. Sulfite and thiosulfate were used as electron accepters by strains ASv26(T), PSv29(T) and LSv54(T), and all strains except PSv29(T) grew with Fe3+ (ferric citrate) as electron acceptor. Chemotaxonomy based on cellular fatty acid patterns and menaquinones showed good agreement with the phylogeny based on 16S rRNA sequences. All strains belonged to the delta subclass of Proteobacteria but had at least 9% evolutionary distance from known sulfate reducers. Due to the phylogenetic and phenotypic differences between the new isolates and their closest relatives, establishment of the new genera Desulfotalea gen. nov., Desulfofaba gen. nov. and Desulfofrigus gen. nov. is proposed, with strain ASv26(T) as the type strain of the type species Desulfofrigus oceanense sp. nov., LSV21(T) as the type strain of Desulfofrigus fragile sp. nov., PSv29(T) as the type strain of the type species Desulfofaba gelida sp. nov., LSv54(T) as the type strain of the type species Desulfotalea psychrophila sp. nov. and LSv514T as the type strain of Desulfotalea arctics sp. nov.