Outer membrane characteristics of Campylobacter jejuni

Abstract

Outer membranes were isolated from type strains and wild-type isolates of Campylobacter jejuni and Campylobacter coli by sodium lauryl sarcosinate extraction, and the polypeptide complement and lipopolysaccharide (LPS) content were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein profiles exhibited by membranes from both species were quite similar, but could be distinguished from the type strain of the genus, C. fetus subsp. fetus CIP5396. The sodium dodecyl sulfate electrophoretograms of C. jejuni and C. coli were dominated by a major polypeptide band. In the reference strain C. jejuni VC74, this polypeptide had an apparent molecular weight of 45,000, was heat modifiable, and was shown to be transmembrane by virtue of its peptidoglycan association and surface exposure. Two other proteins with approximate molecular weights of 37,000 and 73,000 were also surface exposed on C. jejuni VC74 and represented potential surface antigens. The LPS of C. jejuni and C. coli was of low molecular weight, suggesting that serotypic differences due to LPS were based on different carbohydrate compositions of core LPS. In contrast, the LPS of C. fetus CIP5396 exhibited O antigen polysaccharide chains of intermediate chain length. Fragments of outer membranes released during growth of C. jejuni VC74 displayed a polypeptide profile which differed from that of sarcosinate-extracted outer membranes. Radiolabeling demonstrated that the proteins exposed on the surface of this released membrane differed from those exposed on the cell surface and would likely contribute to the antigenic complexity of C. jejuni.