| Summary: | <p>Abstract</p> <p>Background</p> <p>Urease is a virulence factor that plays a role in the resistance of <it>Brucella </it>to low pH conditions, both <it>in vivo </it>and <it>in vitro</it>. <it>Brucella </it>contains two separate urease gene clusters, <it>ure1 </it>and <it>ure2</it>. Although only <it>ure1 </it>codes for an active urease, <it>ure2 </it>is also transcribed, but its contribution to <it>Brucella </it>biology is unknown.</p> <p>Results</p> <p>Re-examination of the <it>ure2 </it>locus showed that the operon includes five genes downstream of <it>ureABCEFGDT </it>that are orthologs to a <it>nikKMLQO </it>cluster encoding an ECF-type transport system for nickel. <it>ureT </it>and <it>nikO </it>mutants were constructed and analyzed for urease activity and acid resistance. A non-polar <it>ureT </it>mutant was unaffected in urease activity at neutral pH but showed a significantly decreased activity at acidic pH. It also showed a decreased survival rate to pH 2 at low concentration of urea when compared to the wild type. The <it>nikO </it>mutant had decreased urease activity and acid resistance at all urea concentrations tested, and this phenotype could be reverted by the addition of nickel to the growth medium.</p> <p>Conclusions</p> <p>Based on these results, we concluded that the operon <it>ure2 </it>codes for an acid-activated urea transporter and a nickel transporter necessary for the maximal activity of the urease whose structural subunits are encoded exclusively by the genes in the <it>ure1 </it>operon.</p>
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