Synthesis and characterization of a 3-hydroxybutyrate and 3-hydroxy-9-octadecenoate copolymer from engineered Halomonas

Abstract

Polyhydroxyalkanoates (PHAs) are a family of biodegradable polyesters accumulated by various microorganisms. The halophilic microorganism Halomonas bluephagenesis has been developed as a production platform strain for various PHAs, chemicals and proteins under open nonsterile and continuous conditions. For the first time, H. bluephagenesis has been engineered to synthesize a copolymer of a short chain length PHA (SCL PHA) and a long chain length PHA (LCL PHA) called, SCL-co-LCL PHA. This study engineered H. bluephagenesis for synthesizing SCL-co-LCL PHA via β-oxidation inhibition and expression of heterologous PHA synthase (PhaC). Sodium oleate was utilized as a structurally related carbon source due to its low cost, long carbon chain length, unsaturated bonds and sustainability. The engineered H. bluephagenesis successfully synthesized copolymers of 3-hydroxybutanoic acid (3HB) and 3-hydroxy-9-octadecenoic acid (3H9Od) on sodium oleate. It could be grown to 8 g L⁻¹ cell dry weight (CDW) containing 51 wt% P(3HB-co-12 mol% 3H9Od) in shake flasks, and 28 g L⁻¹ cell dry weight (CDW) containing 53 wt% P(3HB-co-6 mol% 3H9Od) in 7 L fermenters. Subsequently, the thermal properties of this new PHA were characterized. Finally, chemical click reactions were applied to modify P3HB3H9Od into an organogel, and rare-earth modified fluorescent PHA was successfully prepared.