Outer membrane proteins of Bacteroides fragilis and Bacteroides vulgatus in relation to iron uptake and virulence.

A virulent strain B. fragilis BE1 and an avirulent strain B. vulgatus BE20 were grown in a culture medium with and without the addition of a synthetic chelator (Bipyridyl) to induce iron limitation. Cells grew more slowly under iron stress, although the growth rate of the B. vulgatus strain was more affected under these conditions than the strain of B. fragilis. The outer membrane protein profile of these strains was studied in relation to the iron concentration in the growth medium by means of SDS-polyacrylamide gel electrophoresis. Four proteins, with the apparent molecular weights of 89, 49, 44 and 23.5 kDa, were consistently present in the outer membrane of B. fragilis BE1 grown under iron restricted conditions. In B. vulgatus BE20 cells a 44 and a 23.5 kDa protein were absent and only the expression of an 89 kDa protein was clearly seen under these conditions. The iron regulated proteins, particularly the 44 kDa protein, could be involved to an iron uptake mechanism in B. fragilis. So the presence of these proteins might play an important role in the virulence of this anaerobic bacterium.