In vivo expression technology (IVET) selection of genes of Rhizobium leguminosarum biovar viciae A34 expressed in the rhizosphere

IVET was used to identify genes that are specifically expressed in the rhizosphere of the pea-nodulating bacterium Rhizobium leguminosarum A34. A library of R. leguminosarum A34 cloned in the integration vector pIE1, with inserts upstream of a promoter-less purN:gfp:gusA, was conjugated into purN host RU2249 and recombined into the genome. After removal of colonies that expressed the reporter genes of the vector under laboratory conditions, the library was inoculated into a nonsterile pea rhizosphere. The key result is that 29 rhizosphere-induced loci were identified. Sequence analysis of these clones showed that a wide variety of R. leguminosarum A34 genes are expressed specifically in the rhizosphere including those encoding proteins involved in environmental sensing, control of gene expression, metabolic reactions and membrane transport. These genes are likely to be important for survival and colonization of the pea rhizosphere.