Intra/extracellular electron transfer and energy-dependent Cr(VI) efflux for Gram-negative/positive bacteria mediated by PMo.

Microbial remediation presents a promising approach for combating Cr(VI) pollutants, but the high toxicity of Cr(VI) bottlenecked its practical application. In this study, two-compartmental toxicokinetic (TK) model was constructed to analyze the dynamic Cr(VI) transformation/detoxifying inside Gram-negative/positive bacteria. Phosphomolybdic acid (PMo) could markedly promote the pumping rate (k) and distribution fraction f to accelerate the clearance of toxic substances in compartment two. Zebrafish toxicity and enzyme activity assays further demonstrated the scavenging reactive oxygen species effect of PMo, especially in Gram-negative P. denitrificans, which are more susceptible to heavy metals because they lack peptidoglycan layer, but have lipopolysaccharides that bind to heavy metals. Inhibition (CCCP) assays combined with electrochemical (LSV, DPV and EIS) proved that PMo detoxified Cr(VI) mainly through launching the FDH/Hase-based short electron transport chain, thereby promoting proton-motive force establishment to facilitate energy-dependent efflux pumps. These results provide a reference for the toxicity reduction mechanism of heavy metals assisted with PMo.