Hydrogen-stimulated CO2 fixation and coordinate induction of hydrogenase and ribulosebiphosphate carboxylase in a H2-uptake positive strain of Rhizobium japonicum

Abstract

H2-uptake positive strains (122 DES and SR) and H2-uptake negative strains SR2 and SR3 of Rhizobium japonicum were examined for ribulosebisphosphate (RuBP) carboxylase and H2-uptake activities during growth conditions which induced formation of the hydrogenase system. The rate of 14CO2 uptake by hydrogenase-derepressed cells was about 6-times greater in the presence than in the absence of H2. RuBP carboxylase activity was observed in free-living R. japonicum strains 122 DES or SR only when the cells were derepressed for their hydrogenase system. Hydrogenase and RuBP carboxylase activities were coordinately induced by H2 and both were repressed by added succinate. Hydrogenase-negative mutant strains SR2 and SR3 derived from R. japonicum SR showed no detecyable RuBP carboxylase activities under hydrogenase derepression conditions. No detectable RuBP carboxylase was observed in bacteroids formed by H2-uptake positive strains R. japonicum 122 DES or SR. Propionyl CoA carboxylase activity was consistently observed in extracts of cells from free-living cultures of R. japonicum but activity was not appreciably influenced by the addition of H2. Neither phosphoenolpyruvate carboxylase nor phosphoenolpyruvate carboxykinase activity was detected in extracts of R. japonicum.