Properties of organic acid utilization mutants of Rhizobium leguminosarum strain 300

Nitrogen Fixation Research Group, School of Environmental and Life Sciences, Murdoch University, Murdoch 6150, Western Australia ABSTRACT Summary: Mutants of Rhizobium leguminosarum 300 which were unable to utilize one or more organic acids as growth substrates were obtained by Tn5 mutagenesis. Mutant strain MNF3080 was defective in dicarboxylate transport and was unable to grow on succinate. Strain MNF3085 was defective in phosphoenolpyruvate carboxykinase and hence could not carry out gluconeogenesis. This strain did not grow on pyruvate, succinate, glutamate or arabinose but grew on glucose and on glycerol. Strain MNF3075 was unable to utilize pyruvate; the biochemical lesion in this mutant was not identified. MNF3085 and MNF3075 were symbiotically effective. MNF3080 nodulated peas, but the nodules were ineffective in N 2 fixation and displayed morphological abnormalities. These data support previous findings which suggest that utilization of exogenous dicarboxylates is essential for effective nodule development by R. leguminosarum.