Distribution and Functional Analysis of an ATP-Binding Cassette Transporter-2 in Rhizobium legumionsarum
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Rhizobia are Gram negative, motile, non-sporulating soil bacteria, which interact with legume plants symbiotically to form nitrogen-fixing nodules. In the free-living state, rhizobia dwell in the rhizosphere and surrounding soil where they encounter various environmental stresses such as desiccation stress, nutrient and oxygen limitations, as well as temperature and pH fluctuations. To overcome such conditions, rhizobia adopt different survival mechanisms such as exopolysaccharide (EPS) production, swarming motility and biofilm formation. A previous study identified an ATP binding cassette transporter-2 (ABC) operon, which contains three genes, RL2975-RL2977 (here after referred as RL2975 transporter) that is involved in desiccation tolerance. However, the exact function of the transporter is not known. The study also reported that the transporter genes were present only in the R. leguminosarum and R. etli genomes sequences currently available in publicly accessible databases. Using bioinformatics, PCR and gene expression experiments, I examined the functional activities and diversity of the RL2975 transporter in Rhizobium species. PCR and subsequent DNA sequencing of the amplicons revealed that the transporter is predominantly constrained strains of R. leguminosarum but may also be found in some R. gallicum-like strains. Based on comparison between mutant and wild type, the transporter was not required for persistence in soil and swarming motility.