Biorefinery of volatile fatty acids for the synthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) using Paracoccus sp. TOH: Fermentation performance and metabolic pathway

The residual microbes and uncertain volatile fatty acids (VFAs) components in anaerobic fermentation hydrolysate cause microbial contamination and multi-type polyhydroxyalkanoates (PHA) generation in pure microbial synthesis systems. Meanwhile, the regulation of biosynthesis of poly(3-hydroxybuturate-co-3-hydroxyvalerate) (PHBV), one type of excellent PHA, by re-utilization of waste-organics as carbon substrates is still elusive. In this study, four pretreatment methods for sludge hydrolysate containing 4746 mg-COD·L−1 of VFAs were established to assess the accumulation of PHBV by using Paracoccus sp. TOH as the chassis. Results showed that the autoclaving system exhibited an optimal PHBV concentration of 202.9 mg L−1 with the highest relative abundance of Paracoccus sp. TOH (92.4%). Valeric acid was identified as the primary substrate for 3-hydroxyvalerate accumulation, and the highest PHBV production of 3.76 g L−1 was achieved using 3 g L−1 valeric acid and 5 g L−1 glycerol as co-substrates. The increased carbon metabolism flows through the sequential action of acyl-coenzyme A dehydrogenase and enoyl-coenzyme A hydratase in the fatty acid β-oxidation pathway facilitated PHBV accumulation. This study provides a blueprint for the microbial synthesis of PHBV with oriented acid production from organic wastes. [Display omitted] •Four sludge hydrolysate pretreatment methods produced similar contents of VFAs.•Autoclaving strategy was the optimal pretreatment method for next PHBV synthesis.•PHBV (2.48 g L−1) was produced in a medium containing alone 10 g L−1 valeric acid.•The maximum PHBV production reached 3.76 g L−1 with 46.8 mol% 3HV.•The expression of genes involved in the fatty acid β-oxidation was upregulated.