N 3 oxododecanoyl l hsl 3 oxo c12 hsl

The standards N-butyryl-L-HSL (C4-HSL) and N-(3-oxododecanoyl)-L-HSL (3-oxo-C12-HSL) were purchased from Sigma. Methanol, acetonitrile (HPLC grade), and formic acid (MS grade) were purchased from Fisher Scientific (Loughborough, UK). Acetic acid and ethyl acetate (HPLC grade) were obtained from Guangzhou Chemical Reagent Factory (Guangzhou, China), and ultra-pure water (>18 MΩ/cm) was obtained from a Milli-Q water Elga Maxima water purification system (Merck KgaA, Germany).

AHL signals were tested at 1 µM concentrations and included N-butanoyl-l-homoserine lactone (C4-HSL); N-3-oxo-hexanoyl-l-HSL (3-oxo-C6-HSL), N-3-oxo-octanoyl-l-HSL (3-oxo-C8-HSL), N-3-hydroxyoctanoyl-l-HSL (3-hydroxy-C8-HSL), N-3-oxododecanoyl-l-HSL (3-oxo-C12-HSL), and N-(p-coumaroyl)-l-HSL (p-coumaroyl-HSL) (purchased from Sigma-Aldrich, St. Louis, MO, or the University of Nottingham, Nottingham, United Kingdom). The β-naphthylamide and p-nitroanilide amino acid substrates were purchased from Sigma-Aldrich. Bacto-peptone, Bacto-soytone, and Bacto-tryptone were purchased from Becton, Dickinson, and Company (Franklin Lakes, NJ). The HS dipeptide was purchased from both AnaSpec (Fremont, CA) and Sigma-Aldrich. The tripeptides HSS, SHS, and SSH were custom synthesized by Peptide 2.0 (Chantilly, VA).