Characterisation of the urease gene cluster in Bordetella bronchiseptica

Bordetella bronchiseptica is a common ureolytic mammalian respiratory pathogen. The urease operon of this organism is encoded within an 8.9 kb DNA fragment which contains the structural genes (ureA, ureB and ureC) and accessory genes (ureD and ureG) homologous to other urease genes. Uniquely, the ureE and ureF genes are fused to form a hybrid protein, UreEF, which may result in tighter coordination of the putative functions of the individual accessory genes, nickel donation to the urease active site, and prevention of nickel incorporation until correct formation of the active site, respectively. The operon contains an additional open reading frame, UreJ, found only also in the Alcaligenes eutrophus urease operon. UreJ is also 37% homologous with HupE from Rhizobium leguminosarum bv. viciae, and may potentially be involved in nickel transport. A transcriptional activator, designated Bordetella bronchiseptica urease regulator (BbuR), is located directly upstream and in the opposite orientation to the urease operon. BbuR shares homology with members of the LysR regulatory protein family. LysR proteins have been shown to regulate urease in Klebsiella aerogenes (NAC), and catalase in Escherichia coli (OxyR), which offers the intracellular bacterium protection from phagolysosome damage. A putative BbuR binding site (5'-ATA-N9-TAT-3'), identical to the NAC-binding consensus sequence, was found 27 bp upstream of the urease promoter in B. bronchiseptica. We hypothesise that BbuR controls urease expression which is involved in protection of intracellular B. bronchiseptica from phagolysosomal damage. Comparison of the urease promoter regions of B. bronchiseptica, Bordetella parapertussis ATCC15311 and the urease-negative strain B. pertussis Tohama I revealed no differences in the ureD open reading frame between each species. A cluster of mutations in both B. pertussis and B. parapertussis was found upstream of the urease promoter, in a region proximal to the putative bbuR promoter. The inability of B. pertussis to produce urease may therefore reflect mutations in regulatory elements, and not mutations in the urease locus itself.