Psoralen

The model P. aeruginosa strains PAO1 and PA14, PAO1-ΔlasI, PAO1-ΔrhlI, PAO1-ΔpqsA, 10 clinical strains, and the uracil nutrition-deficient Escherichia coli OP50 were all kept in our laboratory (Zhao et al. 2020 (link)). The used media included lysogeny broth (LB), Mueller–Hinton broth (MHB), M9 minimum growth medium with adenosine (0.1%, w/v) or casein (0.5%, w/v), M8-agar (0.5%, w/v), nematode growth medium (NGM), and peptone-glucose-sorbitol agar medium (PGS). Psoralen, with a purity of 98%, was purchased from Chengdu Alfa Biotechnology Co., Ltd. (Chengdu, China) and dissolved in dimethyl sulfoxide (DMSO) (Chron Chemicals) to a concentration of 100 mM for further usage. The QS signal molecules C12-HSL, C4-HSL, and PQS were purchased from MedChemExpress (Shanghai, China). Bacterial cells were incubated in LB broth from a single colony and cultured overnight (16–18 h) at 37 °C with shaking (180 rpm). Bacterial cells were then adjusted to optical densify of 1.0 at the absorbance of 600 nm (OD₆₀₀ = 1.0) by using sterile saline for further usage.

Xanthotoxin, herniarin, toncarine, bergamottin, oxypeucedanin, biacangelicol, psoralen, isopimpinellin, bergapten, and imperatorin (purity ≥ 98%) were purchased from Chengdu Alfa Biotechnology (Chengdu, China). 5-Geranyloxy-7-methoxycoumarin (purity ≥ 99%) was bought from Extrasynthese (Genay, France). Trioxsalen and 6′,7′-epoxybergamottin (purity ≥ 98%) were obtained from Cayman Chemical Company (Michigan, USA). Citropten (purity ≥ 99%) was purchased from Sigma-Aldrich (St. Louis, MO, USA). LCMS-grade methanol, LCMS-grade water, and HPLC-formic acid were purchased from Sigma-Aldrich (St. Louis, MO, USA). Stock solutions of each standard at a concentration of 10 ppm were prepared by diluting the powder in methanol.