Fine-Tuning Biosynthesis of Biodegradable Poly(3-hydroxybutyrate-co-lactate) with Different Ratios of d-Lactate from Xylose by Engineered Escherichia coli

The toughness and transparency of poly(3-hydroxybutyrate-co-lactate) [P(3HB-co-LA)] depend on its lactate (LA) fraction. In Escherichia coli, LA production can be increased by restricting the activity of the electron transport chain (ETC). As ubiquinone-8 (Q8) is essential to mediate electron transfer, it is one target to modulate the ETC in E. coli. 4-Hydroxybenzoate geranyltransferase (lePGT-1, encoded by the lepgt gene) from Lithospermum erythrorhizon can competitively consume substrates required for the biosynthesis of Q8. Therefore, flexible regulation of LA production can be achieved by controlling the expression level of the lepgt gene to precisely control the flux of the ETC. This strategy was applied for the regulation of the molar percentage (mol %) of the LA fraction in P(3HB-co-LA). Using xylose as a carbon source instead of glucose increased the LA fraction to 10.6–27.7 mol %, and deleting cytochrome oxidase genes further increased the LA fraction to 29.3–41.8 mol %. Finally, the stability and effectiveness of the flexible control strategy were verified by a bioreactor study.