A new species, Porphyromonas circumdentaria, is proposed for pigmented, asaccharolytic strains that were isolated from the gingival margins or mouth-associated diseases of cats. This bacterium is an obligately anaerobic, gram-negative, brown- or black-pigmented, asaccharolytic, nonmotile, nonsporing, rod-shaped organism which does not grow in bile and has a guanine-plus-cytosine content of 40 to 42 mol%. It produces major amounts of acetic, butyric, and isovaleric acids and minor amounts of propionic, isobutyric, and phenylacetic acids as end products of metabolism in cooked meat medium. Glutamate and malate dehydrogenases are present, while 6-phosphogluconate and glucose-6-phosphate dehydrogenases are absent. The major cellular fatty acid is 13-methyltetradecanoic acid (iso-C15:0 acid). P. circumdentaria strains are catalase positive and produce ammonia, and colonies fluoresce under short-wavelength UV light. These strains do not hemagglutinate erythrocytes, exhibit trypsinlike activity, or produce chymotrypsin or alpha-fucosidase. They are heavily piliated and produce a capsule. The type strain is strain VPB 3329 (= NCTC 12469). Bacteroides salivosus (D. N. Love, J. L. Johnson, R. F. Jones, and A. Calverley, Int. J. Syst. Bacteriol. 37:307-309, 1987) is an obligately anaerobic, gram-negative, pigmented, asaccharolytic, nonmotile, rod-shaped organism which does not grow in bile and has a guanine-plus-cytosine content of 42 to 44 mol%. This organism produces major amounts of acetic, butyric, and phenylacetic acids and minor amounts of isobutyric and isovaleric acids as end products of metabolism in cooked meat medium.(ABSTRACT TRUNCATED AT 250 WORDS)