Optimization of Polyhydroxybutyrate Production by Bacillus Species Isolated from Dump Site Soil Using Multiple Linear Regression Analysis

Petrochemical-based plastics cause considerable environmental degradation due to their non-biodegradable properties; however, biodegradable plastics, such as polyhydroxybutyrates (PHBs), provide a sustainable relief to the environment. This study used sugarcane bagasse as a carbon source to synthesize PHB by Bacillus species isolated from dumping site soil. Bacillus velezensis, which displays a high affinity to generate PHB based on the intensity of coloration upon radiation, was selected from 53 isolates. At 30°C, pH 7.5, and 48 hours of incubation, under the ideal conditions resulted in attaining the maximum PHB yield of 50.23% (w/w). Similarly, a predicted PHB yield of 66.05% (w/w) was estimated by a multiple linear regression (MLR) model utilizing ordinary least squares (OLS) regression, which identified temperature, pH, substrate concentration, and incubation time as critical variables. Scanning electron microscopy displayed intracellular PHB granules, and Fourier-transform infrared (FT-IR) analysis indicated the existence of unique PHB functional groups (C–H, CH₂, C=O, and C–O). Tests on biodegradability indicated that soil microorganisms can break down the produced PHB, highlighting the environmental benefits of this research. This study also demonstrates that sugarcane bagasse, an agricultural byproduct, is a cost-effective raw material for PHB synthesis. Additionally, the OLS model provided useful insights for optimizing yield, indicating promise for industrial applications. Future studies should examine other optimization statistical techniques like Response Surface Methodology (RSM) to boost PHB production in complex biological systems. These techniques could also address scalability, economic feasibility, and environmental benefits through cooperation with agro-waste companies and pilot-scale manufacturing activities.