Biorefinery of sugarcane molasses for poly(3-hydroxybutyrate) fermentation and genomic elucidation of metabolic mechanism using Paracoccus sp. P2.

Biorefining sugarcane molasses to produce polyhydroxyalkanoates (PHAs) is an anticipated paradigm for replacing petroleum-based plastics. Nevertheless, there exists a deficiency in excellent chassis and genome resolution for the synthesis of poly(3-hydroxybutyrate) (PHB), which is a typical representative of PHAs. In this study, successive enrichment domestication was employed to screen PHB producers. The isolated species was defined as Paracoccus sp. P2 through taxonomic analysis. Then, a variety of nutrient substrates and physicochemical parameters were tailored to enhance the fermentation capacity. The maximum production of bio-polyester was 4.4 g·L^-1, corresponding to a yield of 0.37 g-PHB·g^-1-glucose. The concentration of PHB produced from 30 g·L^-1 sugarcane molasses was 3.9 g·L^-1, indicating a comparable fermentation performance. Furthermore, three-step condensation of acetyl-CoA and de novo synthesis of fatty acids were identified as the primary PHB accumulation pathways. The fermentation performance and genome investigation were compared with Paracoccus genus. The effective production of Paracoccus sp. P2 might be attributed to its efficient substrate conversion capacity and abundant PHB metabolic network. This study broadened the germplasm resources available for the bioconversion of sugarcane molasses, providing theoretical references for the valorization of high-concentration waste carbon sources.