Regulation of pyruvate carboxylase in Rhizobium etli

Pyruvate carboxylase (PYC) is a biotin-dependent enzyme catalyzing the anaplerotic conversion of pyruvate to oxaloacetate in Rhizobium etli strain CE3. A pyc::Tn5 mutant had severely reduced growth, or failed to grow on sugars, three-carbon organic acids or glycerol, consistent with these substrates being metabolized via pyruvate. Transconjugants expressing a pyc::beta-glucuronidase gene fusion had slightly increased apparent pyc transcription during growth on pyruvate as compared to succinate, similar to the modest carbon source dependent changes in PYC activity reported previously. Biotin supplementation of cultures growing on pyruvate dramatically increased PYC activity but not apparent pyc transcription. Bacteroids isolated from bean nodules did not contain detectable PYC activity while apparent pyc transcription occurred at a moderate level.