BDSF Analogues Inhibit Quorum Sensing-Regulated Biofilm Production in Xylella fastidiosa

<i>Xylella fastidiosa</i> is an aerobic, Gram-negative bacterium that is responsible for many plant diseases. The bacterium is the causal agent of Pierce's disease in grapes and is also responsible for citrus variegated chlorosis, peach phony disease, olive quick decline syndrome and leaf scorches of various species. The production of biofilm is intrinsically linked with persistence and transmission in <i>X. fastidiosa</i>. Biofilm formation is regulated by members of the Diffusible Signal Factor (DSF) quorum sensing signalling family which are comprised of a series of long chain <i>cis</i>-unsaturated fatty acids. This article describes the evaluation of a library of <i>N</i>-acyl sulfonamide bioisosteric analogues of BDSF, <i>Xf</i>DSF1 and <i>Xf</i>DSF2 for their ability to control biofilm production in <i>X. fastidiosa</i>. The compounds were screened against both the wild-type strain Temecula and an <i>rpfF</i>* mutant which can perceive but not produce <i>Xf</i>DSF. Planktonic cell abundance was measured via OD600 while standard crystal violet assays were used to determine biofilm biomass. Several compounds were found to be effective biofilm inhibitors depending on the nature of the sulfonamide substituent. The findings reported here may provide future opportunities for biocontrol of this important plant pathogen.