Valorization of Chickpea agro-waste for microbial γ-Polyglutamic Acid production and circular biorefinery applications using novel Bacillus isolates

Gamma-polyglutamic acid (γ-PGA) is a biodegradable, water-soluble, and non-toxic microbial biopolymer with diverse applications in food, agriculture, medicine, wastewater treatment, and biodegradable materials. However, its commercial production is limited by the high cost of synthetic substrates and downstream processing. In this study, we developed a sustainable and low-cost approach for γ-PGA production using chickpea agro-waste and indigenous bacterial isolates from municipal dumping zones near Sharda University, Greater Noida, India. Among 27 isolates recovered from organic waste-contaminated soil, isolate DZ-7 showed the highest γ-PGA production (24.8 ± 0.92 g/L) under submerged fermentation and was identified as Bacillus subtilis DZ-7 through morphological, biochemical, and 16S rRNA analysis. Chickpea waste fractions were utilized as substrate under solid-state fermentation. Optimization using a one-factor-at-a-time method revealed that moisture content, pH, temperature, glutamic acid supplementation, and inoculum size significantly affected γ-PGA synthesis. A maximum production of 36.8 ± 1.14 g/kg substrate was achieved at 68% moisture content, pH 7.2, 37°C, 2.5% glutamic acid, and 6% inoculum. Characterization by UV–Visible spectroscopy, FTIR, XRD, SEM, and TGA confirmed the structural and thermal properties of γ-PGA. The polymer exhibited a high water-holding capacity (412 ± 14 g/g) and 72.2% biodegradation within 28 days. Fermentation residues also improved mung bean seed germination, indicating their potential as biofertilizers within a sustainable zero-waste biorefinery framework.

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