Genetic regulation of chemotaxis and motility in Rhizobium leguminosarum
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AbstractRhizobium leguminosarum, a nitrogen-fixing root nodule bacterium, has over 20 genes coding MCP-type chemoreceptors, which could playa role in locating host legumes by chemotaxis. Transcriptional gusA fusions were made with the mcpC and mcpD genes, and were used to confirm that the mcp genes are down-regulated in the nodule. Transposon mutagenesis was completed with a mcpC fusion strain to identify possible genes which regulate mcp expression. A free-living mcp regulatory mutant was identified as a bacA mutation, while two mutants which showed less down-regulation in nodules than the wild-type were identified as hutC and a ribitiol transporter mutant. Changes in expression in these mutants in planta were confirmed by examining nodules histologically. The flagellin proteins from a R. leguminosarum strain were isolated and used to produce an anti-flagellar antibody. Immunoblots employing this antibody confirmed that flagella, like MCPs, are down-regulated in nodule bacteria.
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