Having established that strain R2846 can SC79 utilize ferric
ferrichrome as a sole iron source we set out to determine if the fhu gene cluster was involved in the utilization of this iron source. An insertional mutation within the coding sequence of fhuD was successfully constructed as described in the methods section and a mutation derivative Selleckchem AICAR of strain R2846 was designated HI2128. Figure 2A shows that strain HI2128 was unable to grow when supplied with ferric ferrichrome as the sole iron source. The same mutation did not significantly impair the utilization of heme alone (Figure 2A) or either ferric citrate nor ferrous ammonium sulphate in the presence of PPIX (data not shown), indicating that the defect is specific for the ferrichrome molecule rather than impacting the acquisition of the iron moiety or of PPIX. In addition to strain R2846 the fhuD insertional mutation was introduced
into two strains that were positive for the presence of the fhu gene cluster as determined by PCR analyses (Table 2); the two additional strains into which the fhuD mutation was introduced were HI1380 and HI1390 and correctly constructed mutants of each were identified and designated HI2131 and HI2132 respectively. Both strains HI1380 and HI1390 were able to utilize ferric ferrichrome as an iron source while neither PD-1/PD-L1 Inhibitor 3 in vitro of the corresponding fhuD insertion mutants, HI2131 and HI2132, were able to do so (Figures
2B and 2C). Similarly to the data reported for NTHi R2846 neither of the mutant strains were impacted in their ability to utilize other heme and iron sources (Figures 2B and 2C). These data demonstrate that H. influenzae strains containing the fhu operon are able to utilize at least one exogenously supplied siderophore, ferrichrome, as an iron source. Ferrichrome is synthesized by members of the fungal genera Aspergillus, Ustilago and Penicillium, GPX6 and may not represent a readily available iron source in the human nasopharynx. Thus, ferrichrome may not represent the ideal substrate for the fhu locus of H. influenzae which would be utilized relatively inefficiently and this fact may be reflected in the long lag time observed for growth in ferrichrome. However, the fhuBCDA system may function more efficiently to transport other xenosiderophores produced by other microorganisms and further investigations will aim to address this issue. Iron/heme repression of transcription of the fhu genes Since the genes of the identified fhu gene cluster are involved in acquisition of iron the potential role of iron and heme (FeHm) in the regulation of transcription of the genes was determined; since fhuC and r2846.1777 are respectively the first and last genes in the putative operon transcriptional analysis within the operon was limited to these two genes.