Functional analysis of yersiniabactin transport genes of Yersinia enterocolitica

Yersinia enterocolitica O:8, biogroup (BG) IB, strain WA-C carries a high-pathogenicity island (HPI) including iron-repressible genes (irp1-9, fyuA) for biosynthesis and uptake of the siderophore yersiniabactin (Ybt). The authors report the functional analysis of irp6,7,8, which show 98-99% similarity to the corresponding genes ybtP,Q,X on the HPI of Yersinia pestis. It was demonstrated that irp6,7 are involved in ferric (Fe)-Ybt utilization and mouse virulence of Y. enterocolitica, thus confirming corresponding results for Y. pestis. Additionally it was shown that inactivation of the ampG-like gene irp8 did not affect either Fe-Ybt utilization or mouse virulence. To determine whether irp6, irp7 and fyuA (encoding the outer-membrane Fe-Ybt/pesticin receptor FyuA) are sufficient to mediate Fe-Ybt transport/utilization, these genes were transferred into Escherichia coli entD,F and into non-pathogenic Y. enterocolitica, BG IA, strain NF-O. Surprisingly, E. coli entD,F but not Y. enterocolitica NF-O gained the capability to utilize exogenous Fe-Ybt as a result of this gene transfer, although both strains expressed functional FyuA (pesticin sensitivity). These results suggest that besides irp6, irp7 and fyuA, additional genes are required for sufficient Fe-Ybt transport/utilization. Finally, it was shown that irp6, irp7 and fyuA but not irp8 are involved in controlling Ybt biosynthesis and fyuA gene expression: irp6 and/or irp7 mutation leads to upregulation whereas fyuA mutation leads to downregulation. However, fyuA-dependent control of Ybt biosynthesis could be bypassed in a fyuA mutant by ingredients of chrome azurol S (CAS) siderophore indicator agar.