Phenotypic changes resulting from distinct point mutations in the Azospirillum brasilense glnA gene,encoding glutamine synthetase

Sequencing the glnA genes of two chemically induced Azospirillum brasilense glutamine synthetase mutants revealed an Arg-->Cys mutation, corresponding to the glutamate binding site, in one mutant and an Asp-->Asn mutation, corresponding to the ammonium binding site, in the second mutant. The phenotypic changes in these mutants are discussed in relation to their genotypes.