Class I Polyhydroxyalkanoate (PHA) Synthase Increased Polylactic Acid Production in Engineered Escherichia Coli.

Polylactic acid (PLA), a homopolymer of lactic acid (LA), is a bio-derived, biocompatible, and biodegradable polyester. The evolved class II PHA synthase (PhaC1 ) was commonly utilized in the biosynthesis of PLA from biomass. This study tested alternative class I PHA synthase (PhaC ) from sp. USM2 in engineered for the biosynthesis of PLA from glucose. The results indicated that PhaC had better performance in PLA production than that of class II synthase PhaC1 . In addition, the gene was engineered in PLA-producing strains for morphological engineering. The morphologically engineered strains present increased PLA production. This study also tested fused propionyl-CoA transferase and lactate dehydrogenase A (fused Pct /LdhA) in engineered and found that fused Pct /LdhA did not apparently improve the PLA production. After systematic engineering, the highest PLA production was achieved by MS6 (with and ), which could produce up to 955.0 mg/L of PLA in fed-batch fermentation with the cell dry weights of 2.23%, and the average molecular weight of produced PLA could reach 21,000 Da.