Synthetic AHL Compounds Screening

The non-native AHLs examined in this study were synthesized and purified as described previously.^{[15a (link), 16a-c (link)]} A full listing of these compound structures is shown in Figure S1. OdDHL was purchased from Sigma–Aldrich, and BHL was purchased from Cayman Chemical Company. Chlorophenol red-β-D-galactopyranoside (CPRG), the substrate for the β-galactosidase assays, was purchased from Roche. Stock solutions of compounds were prepared in DMSO (at 100 mM) and stored at −20 °C in sealed vials. The amount of DMSO used in small molecule screens did not exceed 1% (v/v). All synthetic compounds were tested in triplicate, and ≥ 3 separate trials were performed using unique cultures. No compound had an effect on bacterial growth over the concentrations tested as gauged by monitoring OD₆₀₀ over the time course of the assays. IC₅₀ and EC₅₀ values were calculated with GraphPad Prism software (v. 4.0) by using a variable slope sigmoidal curve fit.