Opposing selective forces for expression of the gonococcal lactoferrin receptor

Summary All isolates of Neisseria gonorrhoeae express recep- tors that bind human transferrin (Tf). Although lacto- ferrin (Lf) is abundant on mucosa and in purulent exudates, many gonococci do not express an Lf receptor. The naturally occurring Lf receptor deletion mutant FA1090 (LbpB - LbpA - ) is infectious, but a Tf receptor mutant of FA1090 is unable to infect male volunteers (Cornelissen, C.N., Kelley, M., Hobbs, M.M., Anderson, J.E., Cannon, J.G., Cohen, M.S., and Spar- ling, P.F. (1998) Mol Microbiol 27: 611-616). Here, we report that expression of an Lf receptor in the absence of the Tf receptor was sufficient for infection, and that expression of both Lf and Tf receptors resulted in a competitive advantage over a strain that made only the Tf receptor in mixed infection of male volunteers. We confirmed that nearly 50% of clinical isolates do not make an Lf receptor. Surprisingly, about half of geographically diverse Lf - isolates rep- resenting many different auxotypes and porin sero- vars carried an identical lbpB lbpA deletion. Among Lf + strains, all produced the integral outer membrane protein LbpA, but 70% did not express the lipoprotein LbpB. Thus, there are apparently selective pressures for expression of the Lf receptor in the male urethra that are balanced by others against expression of the Lf receptor in niches other than the male urethra.