Biofilm formation by X . citri subsp. citri strain 306 and its derivatives. Biofilm formation in polystyrene 96-well plates (A), glass tubes (B) and on citrus abaxial leaf surfaces (C) was visualized using crystal violet staining. Biofilm formations in glass tubes were quantified by measuring the optical density at 590 nm after dissolution in ethanol-acetone (80:20, v/v). WT: wild-type strain 306; M: gpsX mutant 223 G4 (gpsX-); MV: gpsX mutant 223G4V (gpsX-) with empty vector pUFR053; CM: complemented gpsX mutant C223G4 (gpsX+); CK-: XVM2 medium without inoculation of bacteria. All experiments were performed in quadruplicate and repeated three times with similar results, and only one representative result is presented. Means ± standard deviations are shown.