Neisseria gonorrhoeae heme biosynthetic mutants utilize heme and hemoglobin as a heme source but fail to grow within epithelial cells

Abstract

Many bacterial pathogens, including pathogenic neisseriae, can use heme as an iron source for growth. To study heme utilization by Neisseria gonorrhoeae, two heme biosynthetic mutants were constructed, one with a mutation in hemH (the gene encoding ferrochelatase) and one with a mutation in hemA (the gene encoding γ-glutamyl tRNA reductase). The hemH mutant failed to grow without an exogenous supply of heme or hemoglobin, whereas the hemA mutant failed to grow unless heme, hemoglobin, or heme precursors were present. Growth of the mutants with hemoglobin required expression of the hemoglobin receptor (HpuAB) and was TonB dependent. However, growth with heme required neither HpuAB nor TonB. An fbpA mutant grew normally when either heme or hemoglobin was present in the medium. The heine biosynthetic mutants showed reduced intracellular survival, compared to the parent strain, within A-431 eudocervical epithelial cell cultures. These studies demonstrate that in addition to synthesizing their own heine, N. gonorrhoeae strains are able to internalize and utilize exogenous heine independently of FbpA but appear unable to obtain heme from within epithelial cells for growth.