Mechanism of Cr(VI)-coexistence promoting malathion degradation by Shewanella oneidensis MR-1: Synergistic effects of enhanced membrane permeability and metabolic pathway remodeling

This study elucidates the mechanism by which hexavalent chromium [Cr(VI)] synergistically promotes malathion biodegradation in Shewanella oneidensis MR-1. Exposure to 5 mg/L Cr(VI) significantly enhanced the malathion degradation rate by 2.3-fold, achieving 96.79 % removal within 72 h under optimized conditions (5 % inoculum, pH 6). Analysis of cell membrane parameters combined with microscopic observation techniques indicated that Cr(VI) induced biofilm densification and membrane lipid peroxidation. Metabolomic profiling identified three critical Cr(VI)-activated pathways: (1)tryptophan-mediated redox homeostasis, (2)sulfur assimilation for antioxidant substances biosynthesis, and (3)cofactor biosynthesis for electron transport optimization. These metabolic adaptations increased membrane permeability and accelerated reactive oxygen species diffusion. The findings highlight Cr(VI) as a metabolic modulator that reprograms microbial catabolism via redox signaling, providing a mechanistic basis for developing biocatalysis strategies in multi-pollutant environments.