Valorization of agricultural residues for bioplastic production by bacteria isolated from plastic dumpsites: Integrating waste streams into the circular bioeconomy

• Bacteria from plastic-contaminated soils efficiently produce PHB from sugars & wastes. • Corynebacterium sp . FT(1)-6 & Bacillus sp . GO(10)-6 gave top PHB (∼3.2–3.4 g/L) on cassava. • Micrococcus sp. OO(14)-5 gave highest PHB on mannitol (0.15 g/L), showing substrate efficiency. • FT-IR confirmed PHB functional groups, validating biopolymer from renewable sources. . Polyhydroxybutyrate (PHB) is a biodegradable polymer produced by bacteria under nutrient-limiting conditions, offering a sustainable alternative to petroleum plastics. This study investigated PHB production by bacterial isolates from plastic-contaminated soils. Forty isolates were screened using Sudan Black B, Nile Blue A, and Nile Red; 12 tested positive, and 11 promising strains belonging to genera, Corynebacterium, Bacillus, Micrococcus, Arthrobacter , and Sinomonas were selected for detailed study. Cultivation in nutrient-limiting medium with 2% sugars (fructose, glucose, sucrose, galactose, mannitol) or agro-wastes (cassava wastewater, cassava and potato peels) revealed strain- and substrate-dependent PHB accumulation, peaking at 24–96 h. Micrococcus sp . OO(14)-5 produced the highest PHB content (0.15 g/L) on mannitol, while Corynebacterium sp. FT(1)-6 and Bacillus sp. GO(10)-6 yielded 3.2–3.4 g/L and ∼60% PHB/CDW on cassava wastewater. Other isolates produced >2.7 g/L on peels. Fourier-transform infrared spectroscopy confirmed PHB. These findings highlight low-cost agro-wastes as effective substrates for sustainable PHB production. .