The exact function of the plasmid-encoded citrate synthase is not clear, it could help nodulation by allowing the bacteria to use citrate as a chelator of iron and calcium. acetyl-CoA + H2O + oxaloacetate = citrate + CoA + H(+) Carbohydrate metabolism; tricarboxylic acid cycle; isocitrate from oxaloacetate: step 1/2. Belongs to the citrate synthase family.