Isolation of adenylate cyclase mutants from Rhizobium meliloti deficient in nodulation.

Six Rhizobium meliloti mutants were isolated after Tn5-mediated mutagenesis as resistant to inhibition by a mixture of amino acids (serine, methionine, glycine and leucine). All were defective in adenylate cyclase activity and failed to form nodules in infected roots of Medicago sativa. Furthermore, like other nodulation mutants, they showed altered motility and increased secretion of exopolysaccharides; addition of cAMP to the growth medium abolished some of these phenotypic defects. The possibility that adenylate cyclase participates in the transduction of signals inducing nodulation is discussed.