Process optimization of metabolically engineered Escherichia coliNSK015 fermentation for progressive improvement of 1,3‐propanediol production

Abstract

BACKGROUND: Previously, Escherichia coli NSK015 was developed for high yield of 1,3-propanediol (1,3-PDO) production. To further improve 1,3-PDO concentration, parameters including k L a values with different agitations and impeller numbers, concentrations of coenzyme B12 and feeding strategies during fed-batch fermentation were investigated.RESULTS: In this study, aerobic conditions at 300 rpm agitation and 1 vvm aeration with two Rushton turbine impellers (k L a = 33.6 h −1 ) and the concentration of coenzyme B12 at 7.5 ∼mol L −1 were identified as the best optimized conditions to improve 1,3-PDO production by the strain. With a two-pulsed continuous feeding, E. coli NSK015 produced 1,3-PDO up to 60.3 g L −1 with the 1,3-PDO yield approaching a theoretical maximum of 0.97 g g −1 and productivity of 0.42 g L −1 h −1 in fed-batch fermentation, in which concentration was improved about 60% compared to that of batch fermentation. CONCLUSION: The result indicated the efficiency of E. coli NSK015 in producing 1,3-PDO under optimal aerobic conditions. The strain could even enhance growth and maintain enzymatic activities involved in the 1,3-PDO pathway without utilizing antibiotics, isopropyl ⊎-D-1-thiogalactopyranoside (IPTG) or enriching nutrients. Plasmid instability, high production cost related to medium preparation and purification, and waste disposal were not of concern. This may provide a new insight for large-scale 1,3-PDO production by E. coli NSK015. Additionally, E. coli NSK015 could be a microbial host model for further developing new 1,3-PDO-producing microorganisms regardless of plasmid, inducer, antibiotics and rich nutrients in fermentation medium.

Kinetics-based development of two-stage continuous fermentation of 1,3-propanediol from crude glycerol by Clostridium butyricum

“…In three-stage continuous fermentation, the overall 1,3-PDO productivity could reach 2.89-5.96 g/(L•h) while the yields distributed in 0.483-0.527 g/g (Table 5). The 1,3-PDO concentrations distributed in 73.11-80.50 g/L, which is comparable to some reported values in fedbatch fermentations [8,11,40], such as 80.5 g/L 1,3-PDO by two-pulsed continuous feeding in fed-batch fermentation [23]. Additionally, the main by-product was butyrate with concentrations ranging from 13.05 to 19.54 g/L.…”

“…However, in batch and continuous fermentation, the lower 1,3-PDO concentrations are not suitable for scale-up production. In fed-batch, repeated fed-batch, and sequential fed-batch fermentations, although a satisfactory product concentration can be obtained, it is produced with a complicated feed control strategy in fermentation process, such as pulsed, continuous, and pulsed continuous feeding [23,24]. Continuous fermentations have many striking advantages over batch and fed-batch processes, such as more economical, long-term high productivity without frequent seed culture and energy-intensive sterilization.…”