Robust deltamethrin biodegradation by an alginate-chitosan encapsulated whole-cell biocatalyst with high p-NPA hydrolyzing activity

Deltamethrin (DEL) is a highly potent and persistent pyrethroid insecticide, and its widespread accumulation poses significant ecological risks. While microbial biodegradation targeting ester bond cleavage offers a promising green remediation strategy, free bacterial cells often exhibit poor operational stability and are vulnerable to environmental stresses under realistic conditions. To address this challenge and develop robust biocatalysts, we initially screened for a strain possessing high esterolytic potential using a rapid p -nitrophenyl acetate (p-NPA) hydrolysis assay, identifying Stenotrophomonas sp. Klm2. To enhance its physiological resilience for practical application, whole Klm2 cells were encapsulated within a sodium alginate/chitosan (SA/CTS) dual-network hydrogel composite. Characterization revealed that structural synergy between the biopolymers improved network integrity, providing a protective microenvironment that significantly bolstered the biocatalyst's tolerance to thermal fluctuations, pH shifts, and chemical toxicity compared to free counterparts. The encapsulated Klm2@SA/CTS exhibited remarkable stability, retaining 90.2% of its initial catalytic activity after 7 days of storage at 25 °C and maintaining performance over 8 reuse cycles, with only a 25.9% total activity loss. Crucially, under high DEL loading conditions (200 mg/L), the encapsulated cells outperformed free cells by a wide margin. This enhanced performance was driven by a demonstrated synergistic mechanism coupling rapid physical adsorption onto the hydrogel matrix with sustained intracellular biochemical degradation. This study highlights how rationally engineering the biopolymer microenvironment modulates mass transfer and microbial stability, establishing a reusable, physiologically robust whole-cell platform for efficient pesticide detoxification.