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Background  Urease is a virulence factor that plays a role in the resistance of  Brucella  to low pH conditions, both  in vivo  and  in vitro .  Brucella  contains two separate urease gene clusters,  ure1  and  ure2 . Although only  ure1  codes for an active urease,  ure2  is also transcribed, but its contribution to  Brucella  biology is unknown.    Results  Re-examination of the  ure2  locus showed that the operon includes five genes downstream of  ureABCEFGDT  that are orthologs to a  nikKMLQO  cluster encoding an ECF-type transport system for nickel.  ureT  and  nikO  mutants were constructed and analyzed for urease activity and acid resistance. A non-polar  ureT  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  nikO  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.    Conclusions  Based on these results, we concluded that the operon  ure2  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  ure1  operon.

Brucella abortus ure2 region contains an acid-activated urea transporter and a nickel transport system