Mutagenesis of the carboxy terminal protease CtpA decreases desiccation tolerance in Rhizobium leguminosarum

To better understand the role of proteases in Rhizobium leguminosarum biovar viciae, a gene with homology to the carboxy-terminal protease (CtpA), which belongs to a novel group of serine proteases, was studied. The ctpA gene was cloned and mutated using allelic exchange and a gusA reporter gene was used to study ctpA expression. Mutational analysis shows that ctpA is critical for the viability of R. leguminosarum when cells are grown on complex semi-solid media but is dispensable when cells are grown in complex liquid media and that this is likely due to an increase in susceptibility to desiccation on semi-solid media. The ctpA mutant also displayed an increased sensitivity to detergents, indicating an alteration in the permeability of the cell envelope. This is the first characterization of a ctpA gene within the Rhizobiaceae and the first report of a ctpA mutant that exhibits an increased sensitivity to desiccation.