Response of Neisseria gonorrhoeae to iron limitation: alterations in expression of membrane proteins without apparent siderophore production

Abstract

For acquisition of Fe, an essential nutrient, most microorganisms produce siderophores (low MW Fe-chelating compounds) and membrane proteins to serve as receptors for the Fe-siderophore complexes. The gonococcus does not appear to produce a siderophore, since the quantity of siderophore detected by bioassays of culture supernatants from strains F62 and FA19 was never greater than the amount present in the uninoculated medium. Fe limitation of the laboratory strains F62 and FA19 and 12 recent clinical isolates resulted in the expression of several Fe-repressible membrane proteins. The expression of proteins in the apparent MW range of 70,000-100,000 was strain dependent. All strains expressed 36,000-dalton (36K) and 19.5K proteins. FA19 and F62 were also grown in medium containing Fe sources commonly encountered in vivo (i.e., transferrin, lactoferrin, Hb or hemin). Comparison of growth rates indicates that transferrin and lactoferrin were more readily utilized as Fe sources than hemin and Hb were. Expression of the Fe-repressible proteins varied depending upon the Fe source. Fewer Fe-repressible proteins were observed when cells were supplied with transferrin or lactoferrin than when the cultures were grown with either hemin or HB. The 36K protein was expressed with all 4 Fe sources.