Exploring the Potential of Synechocystis sp. PCC 6803 for P(3HB-co-3HV-co-4HB) Terpolymer Production

The increasing environmental impact of plastic pollution has intensified the demand for sustainable alternatives, such as polyhydroxyalkanoates (PHA). Among different types of PHAs, terpolymer demonstrates superior polymer properties compared to polyhydroxybutyrate (PHB) and its copolymers. Thus, the capability of Synechocystis sp. PCC 6803 for the synthesis of P(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) (P(3HB-co-3HV-co-4HB) terpolymer using sodium acetate (SA), γ-butyrolactone (BL), and sodium valerate (SV) in a two-step process was assessed in this study. To the best of our knowledge, this study reports the production of a terpolymer by any cyanobacterium using carbon sources, expanding the current understanding of cyanobacterial biopolymer biosynthesis. The terpolymer production in the test organism was carried out using polymer accumulation media deprived of nitrogen and phosphorus. The monomer composition of the polymer produced was significantly affected by the concentration of carbon sources. Supplementation of 0.4% SA, 0.01% BL, and 0.01% SV to the cyanobacterial culture medium resulted in the maximum terpolymer accumulation (40.16% dry cell weight). The terpolymer yield (36.33% dcw) decreased when the concentrations of BL and SV were increased to 0.1%, resulting in a terpolymer with higher 3HV and 4HB monomer composition. The purity of the polymer and the mole fraction composition were validated using ¹H-NMR and FTIR analysis. The terpolymer synthesized with varied monomer concentrations was subjected to material characterization using thermogravimetric analysis, differential scanning calorimetry, and mechanical tests. All the terpolymer properties studied here were found to be superior to those of commercial as well as microbially synthesized homo- and copolymers.