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We describe the comparative ultrastructures of bile-sensitive Bacteroides species which were isolated from oral cavities and ferment xylose and arabinose. Reference strains Bacteroides buccae ATCC 33574T(T = type strain), Bacteroides capillus ATCC 33690Tand ATCC 33691, and Bacteroides pentosaceus NP333Tand WPH61 and Bacteroides sp. strains ES42 and ES57 all had an extra surface layer (S-layer) outside the outer membrane. No S-layer was detected in Bacteroides oris ATCC 33573Tand ATCC 27518, Bacteroides oralis, Bacteroides veroralis, or Bacteroides sp. strains ES2759 and ES2834. The deoxyribonucleic acid guanine-plus-cytosine contents and both the malate dehydrogenase and glutamate dehydrogenase mobilities of the strains with an S-layer were identical. We suggest that the oral pentose-fermenting Bacteroides isolates with an S-layer may belong to the same species.

On the basis of phenetic and chemotaxonomic criteria a new nonmotile anaerobic gram-negative rod-shaped bacterium from dental root canals is described. The new species has characteristics in common with species of the genus Bacteroides, but there are also many differences. According to a detailed biochemical analysis the new species is closer to the genus Mitsuokella than to Bacteroides. We propose a new species, Mitsuokella dentalis. The type strain of M. dentalis is strain DSM 3688.