Biopolymer production from sugar beet molasses by Staphylococcus aureus: PHB/PHBV characterization and potential for degradable plastics

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyesters synthesized by various microorganisms, offering promising alternatives to conventional, petroleum-based plastics. In this study, two native Staphylococcus aureus strains isolated from agricultural soil in Qazvin, Iran, were evaluated for their capacity to produce PHAs using glucose and sugar beet molasses—a cost-effective agro-industrial by-product—as carbon sources. Both strains were able to accumulate PHA under varying pH conditions, with a maximum yield of 49.23 % (4.96 g/L) observed using glucose at pH 7.0. When cultivated on sugar beet molasses, PHA accumulation reached up to 23.02 %, indicating the feasibility of using waste-derived substrates. Compositional analysis using Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (¹H NMR) confirmed the production of both poly(3-hydroxybutyrate) (PHB) and the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The detection of 3-hydroxyvalerate units is significant, as PHBV exhibits improved mechanical flexibility and enhanced degradation characteristics compared to PHB alone. The successful biosynthesis of PHBV by S. aureus using an unrefined carbon source highlights its potential for sustainable, low-cost biopolymer production. This study provides a foundation for the valorization of agro-industrial waste into biodegradable materials with tunable properties and contributes to ongoing efforts toward replacing persistent plastics with environmentally responsive alternatives. • Native Staphylococcus aureus strains produce PHAs using sugar beet molasses. • Glucose and molasses supported PHB and PHBV biosynthesis under varying pH. • Maximum PHA yield of 49.23 % achieved at pH 7.0 using glucose as carbon source. • FTIR and ¹H NMR confirmed the production of PHB and PHBV copolymers. • Sugar beet molasses is a promising low-cost substrate for biopolymer production.