The toxicity of 6:2 diPAP to E. coli K12 is regulated by the acrB efflux pump.

Polyfluoroalkyl phosphate esters (PAPs) are a class of emerging per- and polyfluoroalkyl substances, while their bacterial toxicity is lacking. Herein, the wild-type (WT) and Δacriflavine resistance B (acrB) strains of E. coli K12 were exposed to 6:2 diPAP, one frequently detected PAP, respectively. The intracellular concentrations of 6:2 diPAP increased in the absence of acrB. At the individual level, 1 nmol L-1 6:2 diPAP significantly inhibited the growth and elevated reactive oxygen species levels of the WT strain. In the absence of acrB, such inhibitory and stimulating effects were more pronounced at 0.1 and 1 nmol L-1 6:2 diPAP compared with the WT strain. At the population level, biofilm formation was promoted in the WT strain while was inhibited in the ΔacrB strain at 0.1 and 1 nmol L-1 6:2 diPAP. The expressions of S-ribosylhomocysteine lyase, motility protein A and ybaJ followed the same trend as biofilm formation, while those of tryptophanase and haemolysin expression-modulating protein showed opposite trends. The results demonstrate that 6:2 diPAP affected biofilm formation by regulating their expressions. In accordance with biofilm formation, glutathione (GSH) metabolism was activated in the WT strain while was suppressed in the ΔacrB strain by 1 nmol L-1 6:2 diPAP. The defect in biofilm formation of the ΔacrB strain was partly rescued by the addition of four metabolites related with GSH metabolism, consolidating the involvement of GSH metabolism in biofilm formation. Our study shows the indispensable role of acrB in the toxicities of 6:2 diPAP to E. coli at environmentally relevant concentrations.