THE pha GENE CLUSTER OF Brucella abortus INVOLVED IN pH ADAPTATION

LERNER B, ROSET MS, CIOCCHINI AE, IANNINO F, IÑÓN DE IANNINO N.

Pinamar, Buenos Aires, Argentina

Congreso; XLI Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular (SAIB 2005); 2005

Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular (SAIB)

The operon phaABCDEFG in Sinohizobium meliloti code for a K+ secretion system that is involved in the adaptation to pH changes and in symbiosis. In B. abortus a locus highly similar to pha operon of S. meliloti was identified. This cluster of genes is 6 kb and is predicted to encode six membrane-spanning proteins. In this study a polar mutant in phaA/B was constructed and characterized by in vitro and in vivo assays. Growth of the mutant was impaired in define medium at alkaline pH by concentration of added K+ as low as 0.04 M. This phenotype was suppressed with 20 mM sodium acetate added. We studied the multiplication of the Brucella wild type and the mutant in professional and non-professional phagocytes. B. abortus 2308 phaA/B mutant showed differences in the adherence and/or invasiveness in HeLa and J774 cells and less ability to replicate intracellulary during the first hours after infection in HeLa cells. In mouse model the mutant resulted in a reduction of 0.88 and 0.89 Log CFU/spleen at 10 and 30 days post-infection respectively. The indexes of competition between both strains were 7.47 and 1.88 at 10 and 30 days post-infection respectively. These results suggest that the pha operon is important for the homeostatic capacity of pH and for K+ resistance via an K+/H+ antiporter and might be necessary for adaptation to the intracellular lifestyle and virulence.