Valorization of Sugarcane Bagasse for Polyhydroxybutyrate (PHB) Production by Bacillus subtilis SMI3: Process Optimization via Response Surface Methodology and Structural Characterization
DOI:
https://doi.org/10.47430/ujmr.26111.004Keywords:
Bacillus subtilis, Sugarcane bagasse, Polyhydroxyalkanoates, Response Surface Methodology, Central Composite Design, Bioprocess optimizationAbstract
The global transition toward a sustainable circular bioeconomy is heavily dependent on the efficient conversion of lignocellulosic biomass into high-value bioproducts. This research investigated the potential of sugarcane bagasse hydrolysate as a cost-effective carbon feedstock for the biosynthesis of polyhydroxyalkanoates using a resilient Bacillus subtilis strain SMI3. Optimization of fermentation parameters was conducted using both One-Factor-At-a-Time (OFAT) and Response Surface Methodology (RSM) based on Central Composite Design (CCD). The polymers were characterized by Fourier-transform infrared spectroscopy (FTIR). Initial parametric screening via a one-factor-at-a-time approach revealed that the maximum polymer accumulation occurred at an optimal temperature of 35°C, pH of 7.5, and substrate concentration of 3 g/L at 96h of incubation, beyond which significant substrate inhibition was observed. The RSM optimization process successfully enhanced the polymer titer, achieving a maximum experimental yield of 562.05 mg/L at an optimized incubation time of 96 hours and a 3.0 McFarland inoculum standard. Statistical analysis via ANOVA confirmed the high significance of the quadratic regression model (p-value = 0.0105) and a robust correlation coefficient (R2 = 0.7669). Diagnostic metrics, including an Adequate Precision value of 7.466 and a non-significant Lack of Fit (p = 0.2803), validated the model reliability in predicting metabolic outcomes within the design space. Notably, inoculum density emerged as the most influential linear contributor (p = 0.0002), while significant interactive effects were observed between substrate concentration and pH, as well as between incubation time and pH, underscoring the necessity of precise nutritional calibration. Kinetic profiling showed that polymer synthesis peaked during the late exponential phase, followed by a statistically significant decline toward the 120-hour mark. This reduction indicates the activation of intracellular depolymerases, which mobilize the stored polyester as an endogenous energy source once exogenous nutrients become limiting. Collectively, these results demonstrate that Bacillus subtilis SMI3 possesses the metabolic resilience required to navigate the inhibitory landscape of sugarcane bagasse. By successfully integrating statistical optimization with lignocellulosic valorization, this study provides a viable framework for the sustainable production of eco-friendly bioplastics.
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Copyright (c) 2026 Saadatu Ismail Mukhtar, Aminu Bukar, Magashi, A. M., Sani Yahaya, Muhammed Yahuza Gimba, Zainab Salisu Nainna, Nafisa Baita (Author)
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