FIG 4 .

(A) Dose-dependent induction of the Xylella fastidiosa-based DSF biosensor (XfDSF-biosensor strain) by various concentrations of XfDSF and XfDSF2. PhoA activity was measured at 72 h. (B) qRT-PCR analysis of hxfB expression as well as expression of the housekeeping gene rpsO in the Xylella fastidiosa rpfF* strain after 72 h or growth in PD3 broth supplemented with 10 µM XfDSF or 10 µM XfDSF2. rpoD and rpsO were used endogenous control genes. Values shown are the ratios of transcript abundance relative to that of cells exposed to a similar volume of MeOH alone. (C) Biofilm formation at the liquid-air interface of shaken glass tubes by the Xylella fastidiosa rpfF* mutant strain after 24 h of growth in PD3 in broth supplemented with 10 µM XfDSF, 10 µM XfDSF2, or MeOH alone as measured by a crystal violet assay. (D) Induction of the hxfA′::phoA transcriptional fusion in Xylella fastidiosa WT, ΔrpfF, and rpfF* strains by 10 µM XfDSF2 as determined by alkaline phosphatase activity.