Using Agro-Industrial Waste for the Bacterial Biosynthesis of Polyhydroxyalkanoates: A Sustainable Approach for the Production of Biodegradable Plastics

Abstract Synthetic plastics, due to their non-degradability, have become persistent pollutants in the environment, necessitating the development of their sustainable alternatives. Polyhydroxyalkanoates synthesized by various microbial strains under nutrient stress conditions exhibit comparable properties to conventional plastics while offering enhanced biodegradability. Industrial-scale production of polyhydroxyalkanoates remain economically unfeasible due to the high costs associated with conventional carbon feedstocks used for their production. This study aims to investigate the feasibility of utilizing cost-effective carbon substrates derived from Agro-Industrial waste for PHA biosynthesis resulting in the development of biodegradable plastics. Pseudomonas aeruginosa, Bacillus subtilis, Bacillus cereus, and Alcaligenes sp. were employed for PHA biosynthesis using potato and banana peel extracts and dairy industry effluent at 2–10% as alternative carbon sources. Potato peel extract facilitated highest PHA yields, with B. cereus and lowest for P. aeruginosa. Similarly, banana peel extract resulted in highest PHA yield for Alcaligenes sp. Notably, all bacterial strains except P. aeruginosa efficiently utilized 1% potato peel extract, while all strains exhibited optimal PHA synthesis at 2% concentrations of both potato and banana peel extracts. When utilizing dairy industry effluent as carbon source, Alcaligenes sp., B. subtilis, and B. cereus achieved maximum PHA yield at 10% concentration. In contrast, P. aeruginosa exhibited optimal PHA accumulation at lower cheese whey concentrations of 2, 4, and 8%, suggesting species-specific substrate preferences. Experimental conditions were standardized at 37°C and pH 7, which facilitated maximal bacterial growth and PHA accumulation. Furthermore, incubation for 24 to 48 h was identified as the optimal duration for maximum PHA yield in cheese whey-fermentation. FTIR analysis confirmed the structural integrity of the isolated biopolymers, validating their classification as polyhydroxybutyrate. These findings underscore the efficacy of low-cost, agro-industrial waste-derived carbon substrates in enhancing PHA biosynthesis, providing a sustainable and economically viable alternative to traditional petroleum-based plastics. The study highlights the species-specific metabolic capabilities in substrate utilization, emphasizing the potential of optimizing fermentation conditions to maximize PHA yield for large-scale biopolymer production.