MOLECULAR-CLONING, MAPPING, AND REGULATION OF PHO REGULON GENES FOR PHOSPHONATE BREAKDOWN BY THE PHOSPHONATASE PATHWAY OF SALMONELLA-TYPHIMURIUM LT2

Two pathways exist for cleavage of the carbon-phosphorus (C-P) bond of phosphonates, the C-P lyase and the phosphonatase pathways. It was pr eviously demonstrated that Escherichia coli carries genes (named phn) only for the C-P lyase pathway and that Enterobacter aerogenes carries genes for both pathways (K.-S. Lee, W. W. Metcalf, and B, L, Wanner, J. Bacteriol. 174:2501-2510, 1992). In contrast, here it is shown that Salmonella typhimurium LT2 carries genes only for the phosphonatase p athway. Genes for the S. typhimurium phosphonatase pathway were cloned by complementation of E, coli Delta phn mutants. Genes for these path ways were proven not to be homologous and to lie in different chromoso mal regions. The S. typhimurium phn locus lies near 10 min; the E. col i phn locus lies near 93 min, The S, typhimurium phn gene cluster is a bout 7.2 kb in length and, on the basis of gene fusion analysis, appea rs to consist of two (or more) genes or operons that are divergently t ranscribed. Like that of the E, coli phn locus, the expression of the S. typhimurium phn locus is activated under conditions of Pi limitatio n and is subject to Pho regulon control. This was shown both by comple mentation of the appropriate E. coli mutants and by the construction o f S. typhimurium mutants with lesions in the phoB and pst loci, which are required for activation and inhibition of Pho regulon gene express ion, respectively. Complementation studies indicate that the S. typhim urium phn locus probably includes genes both for phosphonate transport and for catalysis of C-P bond cleavage.