Tire-derived 6PPD-quinone promotes conjugative gene transfer through respiratory bioenergetic perturbation

Tire-derived N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) is transported by roadway runoff into urban waters, yet its sublethal effects on microbial gene exchange remain poorly resolved. Here, 5 μg/L 6PPD-Q increased the transconjugant fraction from 0.25% to 0.65% in a lake-water enriched biofilm community and enhanced plasmid transfer in a defined donor-recipient system. Relative to its parent compound 6PPD, 6PPD-Q more strongly altered oxidative phosphorylation, ATP/ADP ratios, and NAD⁺/NADH balance. Molecular simulations indicated membrane partitioning and predicted quinone-site interactions resembling those of ubiquinone analogues, while cyclic voltammetry and partial growth rescue of a ubiB-deficient strain supported quinone-associated redox activity. 6PPD-Q also increased succinate dehydrogenase activity, oxygen consumption, membrane potential, and ATP/ADP ratios. Respiratory-chain and bioenergetic inhibitors attenuated both these responses and the transfer enhancement, linking the phenotype to cellular energy metabolism. Extracellular filament-like structures, migration responses, and appendage-related transcription changed concurrently, although the structures could not be assigned to a specific pilus system. These results support respiratory bioenergetic perturbation as an upstream contributor to 6PPD-Q-enhanced conjugation and identify microbial gene exchange as a water-quality endpoint relevant to tire-contaminated runoff and receiving waters.