In vitro induction of nitrogenase activity in free-living rhizobia by a non-nodulating legume

The effect of cultured carob cell extracts and exudates on acetylene reduction of three different species of Rhizobium, namely R. japonicum IS-33, “cowpea” Rhizobium Tal 169 and R. leguminosarum Tal 619, was studied. The exudates, excreted from plant callus cultures on an agar defined medium promote a synergistic activation of nitrogenase in pure cultures of rhizobia. “ Cowpea” Rhizobium nitrogenase in pure cultures of rhizobia. “ Cowpea” Rhizobium nitrogenase activity was stimulated by a high concentration of sucrose in the medium. Ability of exudates to influence Nase of R. leguminosarum and R. japonicum, respectively, increased in the presence of succinate. Stimulation could also take place when bactéria were grown on medium to which a crude cell extract was added. When the extract was incubated with rhizobia in a minimal nutrient medium a strong synergistic activation of R. leguminosarum and R. japonicum nitrogenase was observed. On this medium the cell extract showed an inhibitory effect on “cowpea” Rhizobium nitrogenase activity