Succinate transport inRhizobium meliloti: Characteristics and impact on symbiosis

The transport of succcinate was studied inRhizobium meliloti M5N1. Succinate accumulation was a saturable function of the succinate concentration, and the apparent Km and Vmax values were respectively 2.9 M and 79 nmoles/min·mg protein. Strong inhibition of succinate transport was observed in the presence of 10 mM DNA and 4 mM azide, whereas arsenate and fluorure had no effect. Fumarate competitively inhibited succinate transport; the Ki value was between 3 and 6 M.A succinate transport mutant ofR. meliloti M5N1 was selected after nitrosoguanidine mutagenesis. It failed to grow on succinate, malate, or fumarate, but grew on arabinose, glutamate, pyruvate, and other carbohydrates. The mutant strain formed white (presumably leghemoglobin deficient) and ineffective nodules, since the acetylene reduction assay showed no nitrogenase activity.