Optimization of dissimilation of glycerol to 1,3-propanediol by Klebsiella pneumoniae in one- and two-stage anaerobic cultures

Abstract

In this study, the optimal conditions of batch and continuous glycerol fermentations by Klebsiella pneumoniae were investigated using the volumetric productivity of 1,3-propanediol (1,3-PD) as an optimization target based on a mathematical model that considers the growth kinetics of multiple inhibitions and the metabolic overflow of substrate consumption and product formation. For batch culture with a given inoculation of 0.1 g biomass l −1, the optimal initial glycerol concentration was found to be 960 mmol l −1, which lead to the highest volumetric productivity (52.6 mmol l −1 h −1) of 1,3-propanediol. For continuous fermentations, the optimal dilution rate and initial glycerol concentration in feed were 0.29 h −1 and 731 mmol l −1, respectively. The corresponding productivity was 114 mmol l −1 h −1 that was more than twice the productivity of an optimal batch culture. A comparison between experimental and computational results of the concentration, yield and productivity of 1,3-propanediol showed that most of the continuous fermentation data were lower than or approached to the calculated values. Stability analysis of continuous cultivations indicated that two regions of multiple states occurred at relatively high concentrations of initial glycerol in feed. One of them approached to the wash-out line. A two-stage continuous process was proposed, in which the first stage was operated at the optimal conditions and the second one was used to consume the residual glycerol in the first one. Model analysis showed that the dilution rate should be much higher in the second stage than in the first one. In terms of the concentration, yield and productivity of 1,3-propanediol, a two-step bioprocess of two bioreactors in series appeared to be more favorable for 1,3-propanediol production than a single bioreactor system with the same volume.