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Two-stage fermentation was normally employed to achieve a high poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] productivity with higher 4HB molar fraction. Here, we demonstrated single-stage fermentation method which is more industrial feasible by implementing mixed-substrate cultivation strategy. Studies on bioreactor scale show a remarkably high PHA accumulation of 73 wt%, contributing to a high PHA concentration and product yield of 8.6 g/L and 2.7 g/g, respectively. This fermentation strategy has resulted in copolymers with wider range of 4HB monomer composition, which ranges from 12 to 55 mol%. These copolymers show a broad range of weight average molecular weight (M w ) from 119.5 to 407.0 kDa. The copolymer characteristics were found to be predominantly affected by the nature of the substrates and the mixture strategies, regardless of the 4HB monomer compositions. This was supported by the determination of copolymer randomness using (13)C-NMR analysis. The study warrants significantly in the copolymer scale-up and modeling at industrial level.

BACKGROUND: The production cost and the material properties of polyhydroxyalkanoate (PHA), a biodegradable plastic are common issues of debate. It has become a constant challenge for researchers to find suitable and relatively cheap carbon substrates. This study has investigated the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)], using a combination of fatty acids and alcohols. The fermentation process described in this study also highlights the potential use of 1-pentanol for the generation of 3HV monomer, in contrast to odd carbon numbered volatile fatty acids, which are known to exert some levels of toxicity towards the cells. RESULTS: Among the various mixtures of fatty acids and 3HV precursors, the mixture of 0.50 wt% C oleic acid and 0.06 wt% C 1-pentanol was found suitable for the production of this copolymer. It was found that Cupriavidus sp. USMAA2-4 could produce up to 56 wt% of P(3HB-co-3HV) with 8 mol% 3HV monomer units. The 3HV monomer composition was also successfully regulated in the range 3-66 mol% by manipulating the culture conditions. The number average molecular weight of the copolymer produced was in the range 217-351 kDa. CONCLUSION: The findings of this study might be used as a platform for scale-up production of 3HV copolymers with different monomer compositions using mixtures of oleic acid and alcohols, namely 1-pentanol for a sustainable production process.

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