Isolation by streptonigrin enrichment and characterization of a transferrin-specific iron uptake mutant of Neisseria meningitidis.

The bactericidal action of the antibiotic streptonigrin is enhanced by large intracellular iron pools. Using this observation, we have utilized a simple enrichment protocol to aid in the isolation of iron uptake mutants of N. meningitidis, based on the relative resistance of iron-starved meningococci to streptonigrin. One such mutant, FAM29, was impaired in its use of transferrin-bound iron; transferrin is the principal iron-binding protein in human plasma. FAM29 retained wild-type ability to utilize iron bound to lactoferrin, heme, or ferric citrate. FAM29 did not produce two iron-repressible outer membrane proteins, of 85,000 and 95,000 daltons, made by the parent strain. However, genetic transformation experiments indicated that the outer membrane protein alterations were not necessary for the transferrin-deficient phenotype.