A psychrotrolerant acetate-oxidizing sulfate-reducing bacterium (strain akvbT) was isolated from sediment from the northern part of The North Sea with annual temperature fluctuations between 8 and 14 °C. Of the various substrates tested, strain akvbT grew exclusively by the oxidation of acetate coupled to the reduction of sulfate. The cells were motile, thick rods with round ends and grew in dense aggregates. Strain akvbT grew at temperatures ranging from -3.6 to 26.3 °C. Optimal growth was observed at 20 °C. The highest cell specific sulfate reduction rate of 6.2 fmol cell-1d-1 determined by the 35 SO42- method was measured at 26 °C. The temperature range of short-term sulfate reduction rates exceeded the temperature range of growth by 5 °C. The Arrhenius relationship for the temperature dependence of growth and sulfate reduction was linear, with two distinct slopes below the optimum temperatures of both processes. The critical temperature was 6.4°C. The highest growth yield (4.3-4.5 g dry weight mol-1 acetate) was determined at temperatures between 5 and 15 °C. The cellular fatty acid composition was determined with cultures grown at 4 and 20 °C, respectively. The relative proportion of cellular unsaturated fatty acids (e.g. 16:1ω7c) was higher in cells grown at 4 °C than in cells grown at 20 °C. The physiological responses to temperature changes showed that strain akvbT was well adapted to the temperature regime of the environment from which it was isolated. Phylogenetic analysis showed that strain akvbT is closest related to Desulfobacter hydrogenophilus, with a 16S rRNA gene sequence similarity of 98.6%. DNA-DNA-hybridization showed a similarity of 32% between D. hydrogenophilus and strain akvbT. Based on phenotypic and DNA-based characteristics we propose that strain akvbT is a member of a new species, Desulfobacter psychrotolerans sp. nov. © Springer Science+Business Media, Inc. 2006.