Capnocytophaga: new genus of gram-negative gliding bacteria. IV. DNA base composition and sequence homology.

Abstract

Isolates of Gram-negative fermentative gliding bacteria which are prominantly cultivated from the subgingival sulcus in association with periodontal lesions have been the subject of a collaborative taxonomic study. Thirty-five oral strains, isolated from various states of periodontal health and disease, were examined for DNA base composition and patterns of DNA sequence homology. The phentotypically similar organism, Bacteroides ochraceus ATCC 27872, as well as two representatives of gliding bacteria in the family Cytophagaceae, Myxococcus fulvus and Sporocytophaga myxococcoides, were included in these comparisons. Mol-percent guanine and cytosine (% G+C) was determined by thermal denaturation. Relatedness was also assessed by interspecific reassociation of DNA measured by the use of a single-strand specific S1 endonuclease. DNA purified from oral gliders, B. ochraceus ATCC27872 and S. myxococcoides contained 33–41% G+C as compared with 67% in DNA from M. fulvus. Three homology groups (designated as 25, 4 and 27) were delineated by DNA homology. Homology at the 77% level was demonstrated between B. ochraceus ATCC 27872 and the oral reference strain 25. Homology group 4 comprised four strains, all of which were isolated from cases of rapidly advancing periodontal disease. The relatively high degree of genetic divergence, observed as intergroup homology levels of less than 25%, supports the naming of three species of Capnocytophaga, C. ochracea, C. sputigena and C. gingivalis by Leadbetter et al. (1979) corresponding to DNA homology groups 25, 4 and 27, respectively.