Deoxyribonucleic acid homologies among strains of Bacteroides melaninogenicus and related species.

Abstract

Saccharolytic, black‐pigmented Bacteroides strains, which at present belong to the species Bacteroides melaninogenicus were classified on the basis of deoxyribonucleic acid (DNA) base ratios and DNA hybridization studies. These strains were divided into several DNA homology groups, which showed no or low mutual DNA homology. A DNA homology group with a percentage guanine plus cytosine (G + C) of 42–43% was formed by three strains of Bact. melaninogenicus subsp. melaninogenicus; the type strain of this subspecies, strain ATCC 25845, had about 60% DNA homology with this group. Strain ATCC 15930, which has been assigned to this subspecies, had a percentage G + C of 47% and showed no DNA homology with the former group. All strains of Bact. melaninogenicus subsp. intermedius had a percentage G + C of 39–45%. A DNA homology group was formed by eight strains of this subspecies. The type strain of Bact. melaninogenicus subsp. intermedius, ATCC 25611, showed relatively low DNA homology with this main DNA homology group. A strain of Bact. melaninogenicus subsp. intermedius serotype C1 showed no DNA homology with the other strains tested. Furthermore two strains labelled ‘Bact. melaninogenicus subsp. levii’ were found to form a distinct DNA homology group. On the basis of the DNA homology results, the strains, which at present are classified in the species Bact. melaninogenicus, were clearly distinguished from strains of Bact. asaccharolyticus and Bact. gingivalis, and also from strains of related non‐pigmented Bacteroides species.