Efficient production of polylactic acid and its copolymers by metabolically engineered Escherichia coli

Polylactic acid (PLA) is one of the promising biodegradable polymers, which has been produced in a rather complicated two-step process by first producing lactic acid by fermentation followed by ring opening polymerization of lactide, a cyclic dimer of lactic acid. Recently, we reported the production of PLA and its copolymers by direct fermentation of metabolically engineered Escherichia coli equipped with the evolved propionate CoA-transferase and polyhydroxyalkanoate (PHA) synthase using glucose as a carbon source. When employing these initially constructed E. coli strains, however, it was necessary to use an inducer for the expression of the engineered genes and to feed succinate for proper cell growth. Here we report further metabolic engineering of E. coli strain to overcome these problems for more efficient production of PLA and its copolymers. This allowed efficient production of PLA and its copolymers without adding inducer and succinate. The finally constructed recombinant E. coli JLXF5 strain was able to produce P(3HB-co-39.6 mol% LA) having the molecular weight of 141,000 Da to 20 g l⁻¹ with a polymer content of 43 wt% in a chemically defined medium by the pH-stat fed-batch culture.