Increased production of polyhydroxyalkanoates with controllable composition and consistent material properties by fed-batch fermentation

The copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with predefined composition was produced by Haloferax mediterranei in fed-batch bioreactor fermentations from volatile fatty acids (VFA). Shake-flask cultivations from a C4:0/C5:0 mix were initially performed at 37 °C and 49 °C with surfactants in order to identify the conditions resulting in the highest copolymer production: PHBV accumulations up to 37% by dry weight and volumetric productivities greater than 5.0 mg L ⁻¹ h ⁻¹ were obtained at 49 °C and at 37 °C with Tween 80. When the cultivation at 37 °C with Tween 80 was scaled-up to a fed-batch bioreactor fermentation, the maximum reported intracellular copolymer content from VFA of 59% by dry weight was produced as well as a twofold increase in productivity to 10.2 mg L ⁻¹ h ⁻¹. A C4:0/C5:0 feed mix containing 44 mol% C5:0 was fed and the PHBV synthesised had the desired composition of 43 mol% HV. The copolymer showed an average molecular weight of 2.1 × 10 ⁶ g/mol and melting temperatures below 102.0 °C. PHBV with bespoke composition and minimal variation in material properties were consistently produced, proving the scalability and reproducibility of the cultivation strategy. The reliable synthesis of copolymers showing minor variations in composition and properties is a step forward towards the widespread use of polyhydroxyalkanoates.