[Effect of short-chain thioesterase deficiency on P(3HB-co-LA) biosynthesis in Escherichia coli].

Polyhydroxyalkanoates (PHAs) have obtained much attention in biomaterial fields due to their similar physicochemical properties to those of the petroleum-derived plastics. Poly(3-hydroxybutyrate-co-lactate) [P(3HB-co-LA)] is one member of the PHAs family, and has better toughness and transparency compared to existing polylactic acid (PLA) and poly[(R)-3-hydroxybutyrate] [P(3HB)]. First, we confirmed the one-step biosynthesis of P(LA-co-3HB) with the lactate fraction of 23.8 mol% by introducing P(3HB-co-LA) production module into Escherichia coli MG1655. Then, the lactate fraction was increased to 37.2 mol% in the dld deficient strain WXJ01-03. The genes encoding the thioesterases, ydiI and yciA, were further knocked out, and the lactate fraction in the P(3HB-co-LA) was improved to 42.3 mol% and 41.1 mol% respectively. Strain WXJ03-03 with dld, ydiI and yciA deficient was used for the production of the LA-enriched polymer, and the lactate fraction was improved to 46.1 mol%. Notably, the lactate fraction in P(3HB-co-LA) from xylose was remarkably higher than from glucose, indicating xylose as a potent carbon source for P(3HB-co-LA) production. Therefore, the deficiency of thioesterase may be considered as an effective strategy to improve the lactate fraction in P(3HB-co-LA) in xylose fermentation.

Efficient poly(3-hydroxybutyrate-co-lactate) production from corn stover hydrolysate by metabolically engineered Escherichia coli.

Poly(3-hydroxybutyrate-co-lactate)[P(3HB-co-LA)], is a biodegradable and biocompatible bioplastic, and the monomeric composition of the copolymer plays an important role in affecting its mechanical properties. Corn stover hydrolysate (CSH), the waste by-product in agriculture, has been considered as an important carbon source for value-added biochemical production. Therefore, the effect of CSH on P(3HB-co-LA) biosynthesis was investigated in this study. Taking CSH as the carbon source, the lactate (LA) fraction in the copolymer reached 7.1 mol% by the engineered stain. The results of shake flask fermentation demonstrated that reducing the activity of electron transport system resulted in a higher LA fraction. Furthermore, we replaced the promoter of the key gene pctth with ldhA gene promoter, so that the expression of pctth gene could be dynamically modulated as well as the lactic acid content changed. This study suggests that CSH is a promising carbon source for the production of biodegradable P(3HB-co-LA).