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Background  In prokaryotes, the ureases are multi-subunit, nickel-containing enzymes that catalyze the hydrolysis of urea to carbon dioxide and ammonia. The  Brucella  genomes contain two urease operons designated as  ure 1 and  ure 2. We investigated the role of the two  Brucella suis  urease operons on the infection, intracellular persistence, growth, and resistance to low-pH killing.    Results  The deduced amino acid sequence of urease-α subunits of operons-1 and -2 exhibited substantial identity with the structural ureases of alpha- and beta-proteobacteria, Gram-positive and Gram-negative bacteria, fungi, and higher plants. Four  ure  deficient strains were generated by deleting one or more of the genes encoding urease subunits of  B. suis  strain 1330 by allelic exchange: strain 1330Δ ure 1K (generated by deleting  ureD  and  ureA  in  ure 1 operon), strain 1330Δ ure 2K ( ureB  and  ureC  in  ure 2 operon), strain 1330Δ ure 2C ( ureA ,  ureB , and  ureC  in  ure 2 operon), and strain 1330Δ ure 1KΔ ure 2C ( ureD  and  ureA  in  ure 1 operon and  ureA ,  ureB , and  ureC  in  ure 2 operon). When grown in urease test broth, strains 1330, 1330Δ ure 2K and 1330Δ ure 2C displayed maximal urease enzyme activity within 24 hours, whereas, strains 1330Δ ure 1K and 1330Δ ure 1KΔ ure 2C exhibited zero urease activity even 96 h after inoculation. Strains 1330Δ ure 1K and 1330Δ ure 1KΔ ure 2C exhibited slower growth rates in tryptic soy broth relative to the wild type strain 1330. When the BALB/c mice were infected intraperitoneally with the strains, six weeks after inoculation, the splenic recovery of the  ure  deficient strains did not differ from the wild type. In contrast, when the mice were inoculated by gavage, one week after inoculation, strain 1330Δ ure 1KΔ ure 2C was cleared from livers and spleens while the wild type strain 1330 was still present. All  B. suis  strains were killed when they were incubated  in-vitro  at pH 2.0. When the strains were incubated at pH 2.0 supplemented with 10 mM urea, strain 1330Δ ure 1K was completely killed, strain 1330Δ ure 2C was partially killed, but strains 1330 and 1330Δ ure 2K were not killed.    Conclusion  These findings suggest that the  ure 1 operon is necessary for optimal growth in culture, urease activity, resistance against low-pH killing, and  in vivo  persistence of  B. suis  when inoculated by gavage. The  ure 2 operon apparently enhances the resistance to low-pH killing  in-vitro .

Brucella suis urease encoded by ure 1 but not ure 2 is necessary for intestinal infection of BALB/c mice