Comparison of strategies for enhanced production of 1,3-propanediol from fermentation broths of Klebsiella pneumoniae

Background: 1,3-Propanediol (1,3-PD) is an important intermediate that is widely used in multiple industries, such as cosmetics, polymers, pharmaceuticals, engine coolants, and heat-transfer fluids. Fermentation is the preferred process for producing 1,3-PD for reasons such as environmental protection and energy saving. Although Klebsiella pneumoniae (K. pneumoniae) appears to be a potential microorganism because of its relatively high productivity, the fermentation of 1,3-PD still has some disadvantages, such as a relatively low yield due to product inhibition compared to chemical synthesis. Therefore, the enhancement of the productivity or yield of 1,3-PD plays a crucial role in the fermentation processes. Methods: In this study, 1,3-PD was produced from glycerol using fermentation broth of K. pneumoniae. Three strategies, including the use of the fed-batch mode, in situ filtration-extraction in hollow-fiber membrane contactors (membrane extraction), and medium dilution, were systematically evaluated and compared. Significant Findings: First, K. pneumoniae was grown in a 5-L fermenter for 12 h, and the productivity (over 12 h) and yield of 1,3-PD production from 40 g/L of glycerol were 1.43 g/(L h) and 0.5, respectively. After the feeding at 9 h, the productivity of 1,3-PD (over 58 h) gradually reached 1.13 g/(L h) at a feeding rate of 24.0 mL/h. After 9 h of in-situ filtration-membrane extraction, the growth of K. pneumoniae was inhibited by the solvent n-hexanol, leading to a lower production and yield. The growth of K. pneumoniae was found to be evidently inhibited in suspension tests when n-hexanol concentration reached 1000 mg/L. In-situ dilution of the culture medium can reduce product inhibition and enhance productivity. For example, at a dilution ratio of 0.75, the amount and yield of the 1,3-PD product were 207.8 g and 0.6 mol/mol, respectively. Finally, using the hybrid process of fermentation and filtration-membrane extraction, a stable 1,3-PD yield with high purity was obtained.