N hexanoyl l homoserine lactone c6 hsl

The in vitro QS inhibitory activity assay was carried out against the C. violaceum CV026. The strain C. violaceum CV026 was inoculated in a 20 mL LB broth medium (NaCl 10 g/L, Tryptone 10 g/L, Yeast Extract 5 g/L) at 37 °C on a rotary shaker (220 rpm) overnight. The culture (0.2 mL) was further mixed with 15 mL of warm molten LB agar (~40 °C) containing kanamycin (Sigma, 0.72mg) and N-hexanoyl-L-homoserine-lactone (C6-HSL) (Sigma, 1.5 μg). The agar was poured into a Petri dish and then punched with a sterile cork borer (Φ 5mm). The methanol solution (10 μL) of tested compounds at the concentration of 40 μg/well were pipetted into each well. Furanone C30 at the concentration of 10 μg/well was employed as the positive control while methanol was used as the negative control. The plates were then incubated overnight at 37 °C.

The leaves of M. bracteata were collected from Fujian Agriculture and Forestry University (Fujian, China). Essential oil (EO) was extracted by steam distillation and then stored at −20 °C.
The microorganisms researched in this study were Dickeya dadantii Onc5, Staphylococcus aureus ATCC25933, Pseudomonas spp. (isolated from Capsicum annuum L), Escherichia coli ATCC25922, Serratia marcescens MG1, Pseudomonas aeruginosa PAO1, Chromobacterium violaceum ATCC31532, and Chromobacterium violaceum CV026, which were stocked in our laboratory. All tested bacteria were incubated in LB broth and grown under conditions of 30 °C, 150 rpm, and 12 h. The swarming motility medium consisted of 1% tryptone, 0.5% NaCl, 0.5% agar, and 0.5% d-glucose. N-Hexanoyl-l-homoserine lactone (C6-HSL) was purchased from Sigma-Aldrich (Shanghai, China). n-Alkanes (C8–C20) standard solution was purchased from Fluka (Shanghai, China).

The AHLs employed in this study were N-Butyryl-DL-homoserine lactone (C₄-HSL; Fluka, Thermo Fisher Scientific, Waltham, US), N-(3-Oxobutyryl)-L-homoserine lactone (3-oxo-C₄-HSL; University of Nottingham, Nottingham, GB), N-Hexanoyl-L-homoserine lactone (C₆-HSL; Sigma-Aldrich, Merck KGaA, Darmstadt, DE), N-Oxohexanoyl-L-homoserine lactone (3-oxo-C₆-HSL; University of Nottingham), N-Octanoyl-L-homoserine lactone (C₈-HSL; Sigma-Aldrich), N-Decanoyl-L-homoserine lactone (C₁₀-HSL; Sigma-Aldrich), N-Dodecanoyl-L-homoserine lactone (C₁₂-HSL; Sigma-Aldrich), N-Tetradecanoyl-DL-homoserine lactone (C₁₄-HSL; Fluka) and N-Octadecanoyl-L-homoserine lactone (C₁₈-HSL; University of Nottingham).
AHLs were clustered in two groups according to their acyl chain length. The short-chain group included C₄-HSL, OC₄-HSL, C₆-HSL, OC₆-HSL and C₈-HSL, whereas the long-chain group included C₁₀-HSL, C₁₂-HSL, C₁₄-HSL and C₁₈-HSL. Stock solutions were prepared for each AHL in acetonitrile. All AHLs were dissolved to a titre of 1 mg/mL and stored at −20°C, except C₁₈-HSL that had to be dissolved to 0.1 mg/mL due to its lower solubility. Prior to each experiment, intermediate dilutions of these stock solutions were prepared in sterile water to generate mixes of the respective short- and long-chain AHLs, reaching a total concentration of 20 μM for each AHL.