AimsTo investigate the role of phosphoenolpyruvate (PEP) carboxylation in cell metabolism in Klebsiella pneumoniae. Methods and ResultsThe effects of deleting pck, which encodes PEP carboxykinase (PCK), and/or ppc, which encodes PEP carboxylase (PPC), on growth, enzyme activity and metabolite formation of Kl.pneumoniae were investigated. A self-regulatory mechanism of PEP carboxylation was found in ppc- or pck-deficient mutants, which resulted in almost no change in succinate formation. However, almost no growth was observed in a ppc- and pck-deficient mutant. Interestingly, only deleting pck affected the energy metabolism and promoted aerobic cell growth. Under micro-aerobic conditions, although there was only a small (81%) increase of 1,3-propanediol production by such pck-deficient mutant during a 2-l fed-batch process, the by-products 2,3-butanediol and acetate significantly decreased by 730% and 548%, respectively, compared with those in the parent strain. ConclusionsPEP carboxylation could be a critical anaplerotic reaction for converting C3 to C4 metabolites in the central metabolism of Kl.pneumoniae. Significance and Impact of the StudyThis study is the first to identify the critical role of PEP carboxylation, as well as those of PPC and PCK, which are responsible for this reaction, in Kl.pneumoniae. In addition, the pck-deficient mutant was proven to be a valuable 1,3-propanediol producer.