Lactate, malate and glutamate dehydrogenase activities of effective and ineffective strains of Rhizobium meliloti

Twelve strains of Rhizobium meliloti were compared on the basis of their D-lactate, L-malate, and L-glutamate dehydrogenase activities in order to note if any correlation existed between the nitrogen-fixing capacities of rhizobial strains and their dehydrogenase specific activities. For this purpose, spectrophoto-metric and electrophoretic techniques were used in conjunction with greenhouse studies. Differences were found between three effective and three ineffective R. meliloti strains in terms of their lactate, malate and glutamate dehydrogenase activities as determined by spectrophotometric means. Effective strains exhibited considerably higher dehydrogenase specific activities for all three substrates studied as compared with the specific activities of these dehydrogenases in ineffective .rhizobial strains. Polyacrylamide gel electrophoresis indicated that major bands of the lactate, glutamate and,to some extent, malate dehydrogenases of effective rhizobia showed a slightly higher mobility than those observed for ineffective strains. Similarities in dehydrogenase banding were observed among several strains of effective and ineffective rhizobia, suggesting a possible close genetic relationship between these strains.