Enhancing 3-hydroxyvalerate concentration in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Pseudomonas aeruginosa...

This study investigated the production of polyhydroxyalkanoates (PHAs) by the alkaliphilic Pseudomonas aeruginosa strain 78B using papermill effluent black liquor as the major aqueous medium component. The strain demonstrated remarkable adaptability to black liquor (containing 34.43% carbon, pH 9.0), accumulating 0.35 ± 0.08 g/L of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) without any nutrients supplementation. Optimization of yeast extract concentration (6 g/L) increased PHA yield to 3.72 ± 0.34 g/L with 3.08 mol% 3 HV content, while volatile fatty acid supplementation significantly enhanced production, with butyric acid yielding the highest PHA accumulation (8.48 ± 0.70 g/L) as primarily poly(3-hydroxybutyrate) homopolymer. Propionic acid supplementation (7.45 ± 0.39 g/L PHA) yielded the highest 3 HV incorporation (29.09 mol%), followed by 2-methylpropionic acid (21.43 mol%) and valeric acid (20.62 mol%), demonstrating precise control of copolymer composition through precursor selection. Comprehensive characterization through GC-MS, FTIR, XRD, EDX-SEM, and thermal analysis confirmed the synthesis of P(3HB) homopolymer and P(3HB-co-3 HV) copolymer with distinct structural and thermal properties. The incorporation of 3-hydroxyvalerate units reduced crystallinity and crystallite size while enhancing thermal stability of the copolymer compared to the homopolymer, with SEM analysis revealing distinct morphological differences between the two polymers. This study provides a sustainable approach to valorize an underutilized industrial waste stream while producing bioplastics with tunable composition and properties for diverse applications including rigid packaging, flexible films, and biomedical materials.