Engineering HT66 for the Biosynthesis of Copolymers Containing 3-Hydroxybutyrate and Medium-Chain-Length 3-Hydroxyalkanoates.

Polyhydroxyalkanoates (PHAs) are promising alternatives to petroleum-based plastics, owing to their biodegradability and superior material properties. Here, the controllable biosynthesis of scl--mcl PHA containing 3-hydroxybutyrate (3HB) and mcl 3-hydroxyalkanoates was achieved in HT66. First, key genes involved in fatty acid β-oxidation, the fatty acid biosynthesis pathway, and the -- operon were deleted to develop a chassis strain. Subsequently, an acetoacetyl-CoA reductase gene and a PHA synthase gene with broad substrate specificity were heterologously expressed for producing and polymerizing the 3HB monomer with mcl 3-hydroxyalkanoates under the assistance of native β-ketothiolase gene . Furthermore, the monomer composition of scl--mcl PHA was regulated by adjusting the amount of glucose and dodecanoic acid supplemented. Notably, the cell dry weight and scl--mcl PHA content reached 14.2 g/L and 60.1 wt %, respectively, when the engineered strain HT11Δ:: was cultured in King's B medium containing 5 g/L glucose and 5 g/L dodecanoic acid. These results demonstrated that can be a platform for producing scl--mcl PHA and has the potential for industrial application.