Production of Bioplastic by Local Strains of Bacillus subtilis using Watermelon Peels as Substrate

Abstract

The increasing environmental contamination caused by the careless disposal of plastic waste has reached alarming levels, with approximately 400 million tons generated globally every year. These synthetic, traditional polymers are not easily biodegradable. This study was therefore undertaken to isolate Bacillus subtilis from soil with the potential to produce bioplastic, specifically Poly-β-hydroxybutyrate (PHB). Soil samples were collected from various locations within Ahmadu Bello University, Zaria, Nigeria, including the Botanical Garden (BG), Fine Art Refuse Dumpsite (FARD), Suleiman Hall Refuse Dumpsite (SHRD), and Faculty of Veterinary Medicine animal paddock (FVM). The spread plate technique was used to isolate B. subtilis on nutrient agar, and the isolates were identified based on their cultural, morphological, and biochemical characteristics. The isolates were screened for PHB production using two methods: the plate assay method and the slide technique with Sudan Black B dye. Submerged fermentation was employed to produce PHB, with watermelon peel serving as the sole carbon source in the production medium. The PHB was extracted using the sodium hypochlorite method, and the quality of the bioplastic was assessed using Fourier-transform infrared (FT-IR) analysis. Four isolates of Bacillus subtilis were obtained from the soil samples (50%), with one isolate from two samples (50%) per location (BG2, FARD3, SHRD2, and FVM4). Screening revealed that all the isolates were capable of producing PHB. Among the isolates, B. subtilis SHRD2 from the Suleiman Hall dormitory produced the highest PHB yield (0.98 g/L) using the watermelon peel substrate, while the isolate from the animal paddock (FVM4) yielded the lowest quantity (0.12 g/L). The identity of the biopolymer as PHB was confirmed by FT-IR spectra, which displayed characteristic wave numbers corresponding to functional groups such as -OH, C-H, C-O, and C=O. This study concludes that local isolates of Bacillus subtilis have significant potential for PHB production using watermelon peels as a sustainable and cost-effective source of carbon and energy.