Polyhydroxyalkanoates: Sustainability, Production, and Industrialization

Polyhydroxyalkanoates (PHA) is a family of biodegradable and biocompatible polyesters with diverse structures. Therefore, PHA is considered as a sustainable biomaterial for the purpose of partially replacing petroleum-based plastics. However, PHA still has a very limited market. High production cost limits large-scale industrial production as well as its wide applications. In order to address this problem, new technologies have been developed to expand PHA diversity. Various PHA types including block copolymers and graft polymers were synthesized. More bacteria that are suitable for industrial production such as Halomonas spp. have been isolated and metabolically engineered for more effective PHA accumulation. Since substrates hold the largest share of production cost, many efforts have been made to use low-cost substrates for PHA production. Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) or P3HB4HB was synthesized in recombinant Escherichia coli from unrelated carbon sources via the construction of anaerobic succinate degradation pathway. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or PHBV was successfully synthesized in Halomonas TD01 from various carbohydrates including glycerol, fructose, maltose, glucose, and sucrose. Engineered Burkholderia cepacia and E. coli can use wooden materials-based xylose for PHBV production. Additionally, Halomonas campaniensis LS21 was selected for the development of a seawater-based open and continuous platform for PHA production from mixed substrates. Novel approaches such as enlarged cell size and CRISPRi technology have also been employed to enhance or control PHA production.