Production of 3-Hydroxypropionic Acid from Glycerol By Metabolically Engineered Klebsiella Pneumoniae L17 in Bioelectrochemical System
Conversions of glycerol to value-added chemicals are one of the interesting topics in bioenergy and biorefinery industry. 3-hydroxypropionic acid (3-HP) is commercially expensive materials due to their usefulness and difficulty of chemical synthesis. Interestingly, 3-HP could be produced biologically by microorganisms such as Klebsiella pneumoniae through glycerol fermentation. In K. pneumoniae, the fermentation of glycerol to 3-HP are proceeded by two enzymes and their cofactors; first glycerol to 3-hydroxypropionaldehyde (3-HPA) by glycerol dehydratase (DhaB) with Coenzyme B12 and then 3-HPA to 3-HP by aldehyde dehydrogenase (ALDH) with NAD+. In the first step, anoxic condition is preferred because not only Coenzyme B12 could be produced in anaerobic condition but also DhaB enzyme could be inhibited by oxygen. However, NAD+ regeneration are needed by oxidizing chemical/reagents (e.g. oxygen and nitrate etc.) for second step. To solve this inconsistency problem, we attempted to apply bioelectrochemical systems for regeneration of NAD+ even in anaerobic condition. And also we metabolically engineered K. pneumoniae L17 for induction and overexpression of aldehyde dehydrogenase (KGSADH, pUC19 vector). Compared to conventional anaerobic fermentation, 3-HP production level was shown significantly high in bioelectrochecmical system. Low level of cellular NADH/NAD+ ratio in K. pneumoniae L17 in bioelectrochecmical system was supported the results. As a result, 3-HP production yield was increased by recombinant K. pneumoniae L17 in bioelectrochemical system. This study is first attempt as the application study of bioelectrochemical system in 3-HP production, in our knowledge. Further study could be applied the recombinant K. pnuemoniae L17 in large scale fed-batch fermentation equipped with bioelectrochecmial system for the examination of commercially applicability.