Characteristics of the outer membrane of selected oral Bacteroides species

The outer membranes from selected oral Bacteroides species were isolated and characterized morphologically, chemically, and physically. Both sucrose density gradient centrifugation and sodium dodecyl sulfate--polyacrylamide gel electrophoresis (SDS-PAGE) revealed outer membranes which varied slightly with the species, as well as showing complex polypeptide patterns after SDS--PAGE. The polypeptide distribution revealed a species-specific pattern; however, there was often a variation within a given species in many minor polypeptide bands, with heat-modifiable minor peptides occurring in nearly all species. Protein-associated carbohydrates occurred in several species. Outer membrane fragments (blebs) recovered by ultracentrifugation of the growth supernatants were either nearly identical to the outer membrane polypeptide patterns, or contained reduced amounts of specific polypeptides, again varying with the species. 125I-labelling of whole cells indicated possible surface exposure for several of the major polypeptides.