Isolation and characterization of glutamate synthase mutants of Azospirillum brasilense

1 Istituto di Anatomia Comparata, Biologia Generale e Genetica, University of Florence, Florence, Italy 2 Istituto di Microbiologia Agraria e Tecnica, University of Florence, Florence, Italy ABSTRACT Six mutants of Azospirillum brasilense Sp6 unable to fix nitrogen have been isolated and characterized. Analysis of the enzymes involved in nitrogen metabolism has shown that the mutants are deficient in glutamate synthase activity ( asm ). They also have a low activity of glutamine synthetase and no or very low nitrogenase activity (assayed by acetylene reduction). In addition, the mutants were unable to grow on various sources of combined nitrogen such as nitrate, nitrite, alanine, histidine, adenine and xanthine.