Bio-Pd(0) diverting electron from CoQ-long chain to FDH/Hase-short chain during sulfamethoxazole degradation

Microbial electron output capacity is critical for organic contaminants biodegradation. Herein, original C. freundii JH could oxidate formate in anaerobic respiration, but lack the ability to degrade sulfamethoxazole (SMX). While the incorporation of Pd(0) could effectively improve the electron output via improving the com-bination between flavins and c-type cytochromes (c-Cyts), increasing the activities of key enzymes (formate dehydrogenase, hydrogenase, F0F1-ATPases), etc. More importantly, the presence of Pd(0) caused the NADH dehydrogenase (complex I) nearly in idle, and triggered the decrease of NADH/NAD+ ratio and increase of H+ -efflux transmembrane gradient, eventually resulting in the electrons diverting from CoQ-involved long respi-ratory chain (decreasing from 91.67% to 36.25%) to FDH/Hases-based hydrogen-producing short chain (increasing from 22.44% to 84.88%), which further intensified the electron output. Above changes effectively launched and guaranteed the high-level SMX degradation by palladized C. freundii JH, alleviating the ecotoxicity of SMX in aquatic and terrestrial environments. These conclusions provided the new view to regulate the mi-crobial electron output behaviors.

Automated summary

Microbial electron output capacity is crucial for the degradation of organic contaminants. The incorporation of Pd(0) has been found to enhance electron output and improve the degradation ability of C. freundii JH towards sulfamethoxazole (SMX). The presence of Pd(0) alters the electron flow, resulting in intensified electron output and reduced ecotoxicity of SMX in the environment.