Metabolic engineering of microorganisms for the production of lactate-containing polyesters

Polylactic acid (PLA) is considered as a biomass-driven alternative to petroleum-based plastic and has biocompatible properties such as biodegradability and low toxicity to humans and environment. Lactic acid, the monomer source of PLA synthesis, is produced by the microbial fermentation, in which microorganisms such as lactic acid bacteria produce (L)-lactate as a major product with the trace amount of (D)-lactate from sugars at almost neutral pH. Metabolic pathways for the production of PLA and PLA copolymers developed in recombinant Escherichia coli. In natural microorganisms, PHA is accumulated as a source of carbon and energy under unfavorable growth conditions; 3-HA-CoAs, the most abundant and easily available metabolites, have been used as substrates for PHA synthesis. Using the metabolic engineering strategies more diverse nonnatural polyesters having novel material properties can be produced from biomass-derived renewable resources by metabolically engineered bacteria, wherein these resources can be pretreated to provide cheap and suitable substrates for microbial fermentations.