High-cell-density fed-batch strategy to manufacture tailor-made P(HB-co-HHx) by engineered Ralstonia eutropha at laboratory scale and pilot scale.

The transition towards a sustainable bioeconomy requires the development of highly efficient bioprocesses that enable the production of bulk materials at a competitive price. This is particularly crucial for driving the commercialization of polyhydroxyalkanoates (PHAs) as biobased and biodegradable plastic substitutes. Among these, the copolymer poly(hydroxybutyrate-co-hydroxyhexanoate) (P(HB-co-HHx)) shows excellent material properties that can be tuned by regulating its monomer composition. In this study, we developed a high-cell-density fed-batch strategy using mixtures of fructose and canola oil to modulate the molar composition of P(HB-co-HHx) produced by Ralstonia eutropha Re2058/pCB113 at 1-L laboratory scale up to 150-L pilot scale. With cell densities >100 g L -1 containing 70-80 wt% of PHA with tunable HHx contents in the range of 9.0-14.6 mol% and productivities of up to 1.5 g L -1  h -1 , we demonstrate the tailor-made production of P(HB-co-HHx) at an industrially relevant scale. Ultimately, this strategy enables the production of PHA bioplastics with defined material properties on the kilogram scale, which is often required for testing and adapting manufacturing processes to target diverse applications.