EXPRESSION OF THE COPB OUTER-MEMBRANE PROTEIN BY MORAXELLA-CATARRHALIS IS REGULATED BY IRON AND AFFECTS IRON ACQUISITION FROM TRANSFERRIN AND LACTOFERRIN

The amino acid sequence of the cell-surface-exposed, 81-kDa CopB outer membrane protein of Moraxella catarrhalis was found to be similar to those of TonB-dependent outer membrane proteins of other gramnegative bacteria. Expression of CopB was affected by the availability of iron in the growth medium, and the extent of overexpression of CopB in resp onse to iron limitation varied widely among the M. catarrhalis strains tested. Wild-type M. catarrhalis strains were found to be able to uti lize ferric citrate, transferrin, lactoferrin, and heme as sources of iron for growth in vitro. However, an isogenic copB mutant was severel y impaired in its ability to utilize transferrin and lactoferrin as so le sources of iron for growth, whereas this same mutant grew similarly to the wild-type parent strain when supplied with ferric citrate as t he iron source. The copB mutant was not significantly different from i ts wild-type parent strain in its ability to bind transferrin and lact oferrin. In addition, the wild-type parent strain and the copB mutant exhibited equivalent rates of uptake of Fe-55 from ferric citrate. How ever, the copB mutant was markedly less able than the wild-type strain to take up Fe-55 from transferrin and lactoferrin. These results indi cate that lack of expression of the CopB protein exerts a direct or in direct effect on the ability of M. catarrhalis to utilize iron bound t o certain carrier proteins.