Purification and Immunochemical Characterization of the Outer Membrane Complex of Bacteroides melaninogenicus Subspecies asaccharolyticus

Abstract

Morphologic study of Bacteroides melaninogenicus subspecies asaccharolyticus by electron microscopy disclosed the presence of a capsule and a cell wall structure otherwise typical of a gram-negative organism. An outer membrane complex was isolated with use of gentle methods. Relative purity of the preparation was confirmed by electron microscopy and by the formation of a single band in a sucrose density gradient. Gel chromatography was used for separation of the major components of the membrane. Antigenicity of the first component, a protein-polysaccharide complex, was demonstrated by agar gel diffusion. Further purification of this fraction showed antigenicity of the polysaccharide component, which cross-reacted with antiserum to another strain of the same subspecies. This component probably represents the capsular antigen and may prove to be the basis for serogrouping. The second membrane fraction differed chemically from the first fraction and represents the lipopolysaccharide component of the outer membrane. Notably, this component lacks 2-keto-3-deoxyoctonate, one of the backbone sugars of aerobic, gram-negative Iipopolysaccharides.