Effect of divalent cations on succinate transport in Rhizobium tropici, R. leguminosarum bv phaseoli and R. loti.

Rhizobium tropici, R. leguminosarum bv phaseoli and R. loti each have an active C4-dicarboxylic acid transport system dependent on an energized membrane. Free thiol groups are probably involved at the active site. Since EDTA inhibited succinate transport in R. leguminosarum bv phaseoli and R. loti, divalent cations may participate in the process; the activity was reconstituted by the addition of Ca(2+) or Mg(2+). However, EDTA had no effect on succinate transport in R. tropici, R. meliloti or R. trifolii strains. Ca(2+) or Mg(2+) had a similar effect on the growth rates of R. tropici and R. leguminosarum bv phaseoli; R. tropici did not require Ca(2+) to grow on minimal medium supplemented with succinate but R. leguminosarum bv phaseoli required either or both of the divalent cations Ca(2+) and Mg(2+). A R. tropici Mu-dI (lacZ) mutant defective in dicarboxylic acid transport, was isolated and found unable to form effective bean nodules.