Siderophore production by pathogenic Neisseria spp.

Previous studies have established the importance of iron acquisition to the growth and virulence of Neisseria meningitidis and Neisseria gonorrhoeae. Although preliminary evidence that the Neisseria spp. produce siderophores has been presented, the exact mechanism of iron acquisition has remained obscure. Siderophore production by N. gonorrhoeae and N. meningitidis was induced in two different low-iron media. The iron-reactive siderophores, "gonobactin" and "meningobactin," were partially purified by ion exchange chromatography followed by extraction with phenol-chloroform-ether or by gel filtration. The compounds were of low molecular weight, their synthesis was repressed by iron in the medium, and they appeared to be hydroxamic acids since they were stimulatory for Arthrobacter flavescens JG-9 (a hydroxamate auxotroph) and gave a positive Csáky reaction for bound hydroxylamine. In the iron form, the compounds had an absorption maximum of approximately 420 nm. Although meningobactin stimulated growth of the gonococcus in low-iron media and vice versa, the homologous activity was more marked, indicating that the compounds, though similar, were probably not identical. As determined by A. flavescens assay the meningococcus produced three to five times more siderophore than did the gonococcus; however, the amount of siderophore present in the culture fluids of even the meningococcus was 100- to 1,000-fold lower than the concentration of hydroxamate siderophores reported to be produced by Bacillus megaterium or Aerobacter aerogenes. Virulent, colony type 1 N. gonorrhoeae produced significantly more gonobactin than did the avirulent colony type 3 gonococci.