ISOLATION OF CARBON-DEPRIVATION AND NITROGEN-DEPRIVATION-INDUCED LOCIOF SINORHIZOBIUM-MELILOTI 1021 BY TN5-LUXAB MUTAGENESIS

Soil bacteria, such as Sinorhizobium meliloti. are subject to variatio n in environmental conditions, including carbon- and nitrogen-deprivat ion. The ability of bacteria to sense changes in their environment and respond accordingly is of vital importance to their survival and pers istence in the soil and rhizosphere. A derivative of Tn5 which creates transcriptional fusions to the promoterless luxAB genes was used to m utagenize S. meliloti 1021 and 5000 insertion mutants were subsequentl y screened for gene fusions induced by selected environmental stresses . The isolation of 21 gene fusions induced by nitrogen-deprivation and 12 induced by carbon-deprivation is described. Cloning and partial DN A sequence analysis of the transposon-tagged loci revealed a variety o f novel genes, as well as S. meliloti genes with significant similarit y to known bacterial loci. In addition, nodule occupancy studies were carried out with selected Tn5-luxAB insertion mutants to examine the r ole of the tagged genes in competition.