Metabolic engineering of escherichia coli for the production of L-Lactic Acid and 1,2-Propanediol

Abstract

C3 chemicals have been known as useful materials for its various applications in industry. There has been much effort to produce three carbon compounds via microbial process instead of petroleum-based chemical process due to environmental problem and shortage in petroleum resource. Here we describe methods for the production of C3 compounds (e.g. L-lactic acid and 1,2-propanediol) by metabolic engineering of Escherichia coli based on rational approach. E. coli was metabolically engineered for production of optically pure L-lactic acid using glucose. We investigated two kinds of L-specific lactate dehydrogenase (L-ldh) genes from Lactobacillus acidophilus and Lactobacillus brevis and found that L-ldhL. acidophilus was desirable for the production of L-lactate with little amount of by-products in E. coli. For the conversion of pyruvate to L-lactate preventing the production of D-lactate, indigenous lactate dehydrogenase (ldhA) gene was deleted in all of E. coli strains used in this study. We optimized the fermentation conditions varying gases for anaerobic atmosphere and attempting dual-phase fermentation for better glucose uptake system in E. coli. In addition, we further examined the effect of deleting alcohol dehydrogenase (adhE) gene on L-lactic acid production. The resulting ldhA strain produced 56.5 g/L of lactic acid from 74.8 g/L glucose in 35 h, representing a 75.5% conversion and a productivity of 1.61 g/L/h, at a yield of 1.52 mol/mol glucose. This is the best conversion rate and yield yet reported in E. coli. Also the resulting E. coli ldhA adhE strain produced 31.4 g/L of lactic acid from 31.9 g/L of glucose, representing a 98.4% conversion with trivial amount of by-products as well. This is the best yield yet reported in L-lactic acid producing microorganisms including Lactobacillus species and yeasts. The optical purity of the L-lactic acid was more than 99%. We further attempted to produce 1,2-propanediol in E. coli utilizing aforementioned L-lac...