Biopolyester Production Using Fruit Wastes as a Substrate by Soil Bacteria

Abstract The global dependence on petroleum-based plastics has led to severe environmental challenges due to their non-biodegradability and persistence in ecosystems. Biopolyesters, particularly polyhydroxyalkanoates (PHAs), have emerged as promising biodegradable alternatives due to their microbial origin, biocompatibility, and sustainable nature. The present study focused on the isolation and characterization of soil bacteria capable of synthesizing biopolyesters using fruit wastes—apple, orange, and banana peels—as renewable and cost-effective carbon substrates. Soil enrichment was performed through mulching with fruit and organic waste to stimulate the proliferation of biopolymer-producing bacteria, thereby enhancing the presence of naturally efficient PHA-accumulating strains in the soil environment. Primary screening for biopolyester producers was performed using Sudan Black B dye, while confirmatory screening employed Nile Blue A. Among twelve isolates, seven showed positive results for biopolymer accumulation, confirming their PHA-producing capability. Quantitative analysis using E ₂ medium revealed that isolates MS-5 and MS-7 have the highest polyester production efficiencies, highlighting their superior metabolic potential. Subsequent fermentation experiments using fruit wastes as sole carbon sources demonstrated that apple peels provided the most favorable substrate for polyester yield, followed by orange and banana peels. The strain MS-7 produced quantities of polyester comparable to the positive control Ralstonia eutropha MTCC1285, further supporting its suitability as an efficient biopolymer-producing organism. Phylogenetic identification through 16S rRNA sequencing confirmed that MS-7 showed 99.83% sequence similarity with Bacillus sp ., validating its genetic affiliation with this genus and supporting the accuracy of its taxonomic placement. Extraction of biopolyester was optimized through a novel sonication-assisted method employing ethylene carbonate, which achieved comparable yields to conventional chloroform extraction but with significantly reduced toxicity and cost, demonstrating a more sustainable and environmentally safe extraction approach. Fourier Transform Infrared Spectroscopy (FTIR) analysis confirmed the presence of functional groups characteristic of polyhydroxybutyrate (PHB), validating the polymer identity, although slight intensity differences indicated minor impurities in the extracted sample. Plasmid curing experiments using ethidium bromide demonstrated that the biopolyester synthesis ability of isolates was chromosomally encoded rather than plasmid-mediated, indicating stable inheritance of the trait.