Characterization of Bacillus pacificus KUMBNGBT-39-Derived Polyhydroxybutyrate and Impact of Physicochemical Factors on its Production

Abstract

The extensive use of various chemicals in synthetic plastics is toxic and threatens the biosphere. To address this, the study aimed to isolate, screen, characterize, optimize, and quantify polyhydroxybutyrate (PHB)-producing bacteria using cost-effective residues. Isolated from a landfill site, the Gram-positive, rod-shaped, spore-forming, motile bacterium with intracellular PHB granules was identified as Bacillus pacificus based on phenotypic and genotypic characteristics. Optimal PHB production parameters included a nutrient broth medium, 72 h of incubation, a temperature of 37° C, a pH of 7.0, glucose as the carbon source, ammonium chloride as the nitrogen source, and a carbon-to-nitrogen ratio of 4:1, resulting in a 1.42-fold PHB production increase. B. pacificus was also cultured on various low-cost substrates. Among the oil wastes, feedstock showed the highest PHB production (1.983 ± 0.005 g/L) and among agricultural residues, the maximum PHB was obtained from rice bran (1.626 ± 0.01 g/L). UV–visible spectrophotometric, FT-IR, and HR-LCMS analysis of extracted PHB confirmed characteristics of PHB molecules (ʎ-max at 210 nm, functional groups between 1152 and 2925 cm⁻¹). The ¹H NMR analysis revealed distinct signals for protons resonating at aliphatic CH₃ proton groups, bridged CH protons, and shielding CH₂ proton regions that matched PHBs. Thermal gravimetric analysis (TGA) and direct scanning colorimetric (DSC) analysis revealed 89.4% degradation and melting temperature at 124.1 °C for the extracted PHB compound.