PATHWAY ANALYSIS OF GLYCEROL FERMENTATION BY KLEBSIELLA-PNEUMONIAE - REGULATION OF REDUCING EQUIVALENT BALANCE AND PRODUCT FORMATION

The method of metabolic pathway stoichiometry was used to analyze the fermentation of glycerol to 1,3-propanediol by Klebsiella pneumoniae D SM 2026, with particular emphasis on the regulation of hydrogen format ion and balance of reducing equivalents (NADH2). Under conditions of g lycerol limitation, H-2 formation was found to be higher than the maxi mum amount that could be generated from the splitting of pyruvate to a cetyl-CoA. Simultaneously, a lower recovery of reducing equivalents wa s found in the reduced product 1,3-propanediol. Under conditions of gl ycerol excess, formation of H-2 was drastically reduced and a surplus of NADH2 was generated for the formation of 1,3-propanediol. These fin dings indicate the existence of enzymes in K. pneumoniae that transfer reducing equivalents from NADH2 to H-2 and 1,3-propanediol flexibly. The physiological meanings of these regulatory mechanisms are discusse d from the viewpoint of bioenergetics and product inhibition. Taking t hese regulation mechanisms into account, the maximum energy and produc t yields of this fermentation were calculated, which agreed well with experimental results. A corrected NADH2 balance equation was derived w hich can be used to calculate the formation of hydrogen under differen t conditions.