3oc8hsl

Pure C6HSL, 3OC6HSL, and 3OC12HSL were obtained from Shanghai UDChem Technology Co., Ltd. 3OC8HSL was purchased from Sigma Aldrich Chemicals Co., Ltd (Shanghai, China). The chemical structures of various N-acyl homoserine lactones (AHLs) used in this study are shown in Supplementary Figure S1. Different antibiotics—ampicillin (Amp, 50 mg⋅mL^–1), chloramphenicol (Cm, 30 mg⋅mL^–1), tetracycline (Tc, 5 mg⋅mL^–1), streptomycin (Str, 50 mg⋅mL^–1), gentamicin (Gen, 50 mg⋅mL^–1), and kanamycin (Kan, 50 mg⋅mL^–1)—were used in antimicrobial susceptibility tests. Pesticide streptomycin (98% active ingredient) was used as a positive control at a concentration of 3.3 g⋅mL^–1. Bacterial strains and plasmids used in this study are presented in Table 1.
The bacterial strain was cultured in minimal salt medium (MSM) [composition (g⋅L^–1): (NH₄)₂SO₄ 2.0, Na₂HPO₄⋅12H₂O 1.5, KH₂PO₄ 1.5, MgSO₄⋅7H₂O 0.2, CaCl₂⋅2H₂O 0.01, FeSO₄⋅7H₂O 0.001, pH 6.5] and Luria-Bertani medium (LB) [composition (g⋅L^–1): Yeast extract 5.0, Tryptone 10.0, NaCl 10.0, pH 7.0] (Chen et al., 2011a (link)). Minimal medium (MM) [composition (g⋅L^–1): (NH₄)₂SO₄ 2.0, MgSO₄⋅7H₂O 0.2, CaCl₂ 0.01, FeSO₄ 0.005, MnCl₂ 0.002, K₂HPO₄ 10.5, KH₂PO₄ 4.5, mannitol 2, glycerol 2, pH 6.5] was used for detecting AHL (Liu et al., 2017 (link)). Agar (15 g⋅L^–1) was used to solidify the medium. Media were sterilized at 121 °C for 20 min.

The following synthetic AHLs (Sigma-Aldrich) were used at a final concentration of 25 μM to evaluate the AHL degradation activity of PQQ-42 and PQQ-44: C4-HSL (N-butyryl-DL-homoserine lactone), C6-HSL (N-hexanoyl-DL-homoserine lactone), 3-O-C6-HSL (N-3-oxo-hexanoyl-DL-homoserine lactone), C8-HSL (N-octanoyl-DL-homoserine lactone), 3-O-C8-HSL (N-3-oxo-octanoyl-DL-homoserine lactone), C10-HSL (N-decanoyl-DL-homoserine lactone), 3-OH-C10-HSL (N-3-hydroxydecanoyl-DL-homoserine lactone), C12-HSL (N-dodecanoyl-DL-homoserine lactone), 3-O-C12-HSL (N-3-oxo-dodecanoyl-DL-homoserine lactone) and C14-HSL (N-tetradecanoyl-DL-homoserine lactone). Briefly, cultures of the two A. stellipolaris strains (OD₆₀₀ 1.5) were mixed with AHLs at the above mentioned final concentration. The mixtures (500 µl of culture supplemented with 0.5 µl of each synthetic AHL) were incubated at 25 °C for 16, 24 and 48 hours, and the remaining AHLs were detected using a well diffusion agar-plate assay technique described elsewhere^{24 (link)} with the aid of the biosensors C. violaceum CV026 and A. tumefaciens NTL4 (pZLR4). The diameters of the colored haloes were measured and compared to controls to determine the percentage of signal molecules remaining in each case. These assays were carried out in triplicate.