A facultatively psychrophilic bacterium, strain 4-22T, was isolated from a cold current off the Monbetsu coast of the Okhotsk Sea in Hokkaido, Japan. The isolate was a rod-shaped facultative anaerobe that reduced nitrate to nitrite and hydrolysed starch, DNA and alginic acid, but not chitin or gelatin. The isolate grew at 0 degrees C, but not at 26 degrees C; the optimum growth temperature was 14-16 degrees C. NaCl was required for growth. The DNA G+C content was 43.5 mol%. The whole-cell fatty acids consisted of significant amounts of an unsaturated fatty acid, C16:1, and a saturated fatty acid, C16:0. A polyunsaturated fatty acid, docosahexaenoic acid (C22:6), was also detected (1.6%). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain 4-22T was closely related to Psychromonas antarctica (95.7% similarity). DNA-DNA hybridization revealed a relatedness of 31% between strain 4-22T and P. antarctica. Based on physiological and biochemical characteristics and the phylogenetic position as determined by 16S rRNA gene analysis and DNA-DNA relatedness, it is concluded that the isolate represents a novel species, for which the name Psychromonas marina sp. nov. is proposed. The type strain is 4-22T (= JCM 10501T = IAM 14899T = NCIMB 13792T).