THE HMU LOCUS OF YERSINIA-PESTIS IS ESSENTIAL FOR UTILIZATION OF FREEHEMIN AND HEME-PROTEIN COMPLEXES AS IRON SOURCES

Yersinia pestis strains utilize haem and several haem-protein complexe s as sole sources of iron. In this study, the haemin uptake locus (hmu ) of Y. pestis KIM6+ was selected from a genomic library by transducti on into an Escherichia coli siderophore synthesis (entC) mutant. Recom binant plasmids containing a common 16 kb BamHI insert were isolated t hat allowed E. coli entC to use haemin as an iron source. An 8.6 kb re gion of this insert was found to be essential for haemin utilization a nd encoded at least five proteins with molecular masses of 79/77, 44, 37, 35, and 30/27.5 kDa. A 10.9 kb Clal fragment containing the hmu lo cus showed varying degrees of homology to genomic DNA from Yersinia ps eudotuberculosis, Yersinia enterocolitica, and other genera of Enterob acteriaceae. An E. coli hemA aroB strain harbouring cloned hmu genes u sed haemin as both an iron and porphyrin source but only on iron-poor medium, suggesting that haemin uptake is tightly iron regulated. Addit ionally, haemoglobin and myoglobin were used as iron sources by an E. coli entC (pHMU2.2) strain. Deletion of the hmu locus from Y. pestis K IM6+ chromosome generated a mutant that grew poorly on iron-depleted m edium containing free haemin as well as mammalian haem-protein complex es including haemoglobin, haemoglobin-haptoglobin, myoglobin, haem-hae mopexin, and haem-albumin unless it was complemented with cloned hmu g enes.