Strain 15(T) is a novel spore-forming, sulfate-reducing bacterium isolated from a permanently cold fjord sediment of Svalbard. Sulfate could be replaced by sulfite or thiosulfate. Hydrogen, formate, lactate, propionate, butyrate, hexanoate, methanol, ethanol, propanol, butanol, pyruvate, malate, succinate, fumarate, proline, alanine and glycine were used as electron donors in the presence of sulfate. Growth occurred with pyruvate as sole substrate. Optimal growth was observed at pH 7.1-7.5 and concentrations of 1-1.5 % NaCl and 0.4 % MgCl(2). Strain 15(T) grew between 26 and 46.5 degrees C and optimal growth occurred at 44 degrees C. Therefore, strain 15(T) apparently cannot grow at in situ temperatures of Arctic sediments from where it was isolated, and it was proposed that it was present in the sediment in the form of spores. The DNA G+C content was 48.9 mol%. Strain 15(T) was most closely related to Desulfotomaculum thermosapovorans MLF(T) (93.5 % 16S rRNA gene sequence similarity). Strain 15(T) represents a novel species, for which the name Desulfotomaculum arcticum sp. nov. is proposed. The type strain is strain 15(T) (=DSM 17038(T)=JCM 12923(T)).