Green synthesis of silver nanoparticles from Bacillus subtilis-mediated feather hydrolysate: antimicrobial, larvicidal against culex pipiens, and anticancer activities

This study presents a novel dual-stage bioprocessing approach that transforms poultry feather waste into multifunctional silver nanoparticles (FWH-AgNPs) with enhanced bioactivity. Bacillus subtilis degradation of feather waste produced bioactive hydrolysate (FWH) with dramatically altered chemical composition, generating novel compounds including 9,12,15-octadecatrienoic acid methyl ester (25.66%) and cyclopropaneoctanoic acid methyl ester (23.02%). The FWH effectively synthesized spherical AgNPs (30-69 nm) with strong colloidal stability (-44.5 mV zeta potential) and characteristic surface plasmon resonance (420 nm). FWH-AgNPs demonstrated superior antimicrobial efficacy with 4-eightfold improved minimum inhibitory concentrations against Pseudomonas aeruginosa (125 μg/mL), methicillin-resistant Staphylococcus aureus (250 μg/mL), Aspergillus brasiliensis (275 μg/mL), and Candida albicans (125 μg/mL). Comparable enhancements were also observed for Serratia marcescens (300 μg/mL) and Bacillus cereus (325 μg/mL), further confirming the broad-spectrum antimicrobial potential of FWH-AgNPs. Anticancer evaluation revealed selective cytotoxicity toward MCF-7 breast cancer cells (IC₅₀: 294.7 μg/L) with favorable selectivity index (2.68) over normal fibroblasts. Optimized FWH-AgNPs achieved 87.38% larvicidal mortality against Culex pipiens, validated through Box-Behnken methodology. Mechanistic studies revealed systematic disruption of larval metabolism, including protein depletion, carbohydrate exhaustion, and acetylcholinesterase inhibition, coupled with severe midgut epithelial damage. Molecular docking identified α1-sitosterol as the primary bioactive compound with strong binding affinities to antimicrobial targets (-7.1 to -7.4 kcal/mol) and cancer receptors (-7.0 to -9.5 kcal/mol). This integrated approach successfully addresses environmental waste management while generating high-value nanomaterials for biomedical and vector control applications, establishing a new paradigm for circular bioeconomy applications.