It is well known that environmental and genetic perturbations have major effects on the metabolic behavior of cells. In this work, a model that utilizes existing knowledge of oxygen and redox sensing/regulatory system to assist elementary flux modes (EFMs) has been developed and was carried out to predict the metabolic potential of Klebsiella pneumoniae for the production of 1,3-propanediol (1,3-PD) under anaerobic and aerobic conditions. It was found that the theoretical optimal 1,3-PD yield could reach to 0.844 mol mol(-1) if the pentose phosphate pathway (PPP), and transhydrogenase had a high flux under anaerobic condition. However, PPP had little influence on the theoretical 1,3-PD yield, and the flux through tricarboxylic acid (TCA) cycle was high under aerobic conditions. In addition, the effect of oxygen level on the 1,3-PD and biomass was further analyzed. (C) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 25: 103-115, 2009