Efficient 1,3-propanediol Production by Fed-Batch Culture of Klebsiella Pneumoniae : The Role of pH Fluctuation

TLDR: A self-protection mechanism in K. pneumoniae cells switch the metabolic pathways responding to environmental pH changes, which was proposed and fulfilled under the pH-stat fed-batch strategy under the periodical low or high pH stress.

Abstract: The fermentative production of 1,3-propanediol (1,3-PD) by Klebsiella pneumoniae under different fed-batch strategies was investigated. pH-stat fed-batch strategies proved to be not effective for economical 1,3-PD production for the existence of relatively high concentration of byproducts and residual glycerol at the end of the fermentation. However, in the pH-stat fed-batch strategy, an important phenomenon was observed that the yields of two main byproducts, 2,3-butanediol and lactic acid, were closely related to pH value. The dominant byproduct was 2,3-butanediol at a pH value of 5.0 to 6.5 but changed to be lactic acid at a pH value of 7.1 to 8.0. Based on the analysis of the phenomenon, a self-protection mechanism in K. pneumoniae, namely that the growing K. pneumoniae cells switch the metabolic pathways responding to environmental pH changes, was proposed. Thus a kind of feeding strategy was further applied during which the pH value was fluctuated between 6.3 and 7.3 periodically by feeding glycerol-ammonia mixture and sulphuric acid to make the metabolic pathways of 2,3-butanediol and lactic acid sub-active under the periodical low or high pH stress. At last, efficient 1,3-PD production was fulfilled under this fed-batch strategy, and the best results were achieved leading to 70 g/l 1,3-PD with a yield of 0.70 mol/mol glycerol and productivity of 0.97 g/l/h, while the two main byproducts and residual glycerol were under low concentrations.