2.6 Detection of biofilm
WH1, mutant strains and complementary strains were cultured on LB agar plates, then the morphology of colonies were observed by microscope. Robust pellicles (floating biofilms) were determined in multiwell (24-well) plates with 2 ml LB medium each well [37]. Briefly, 20 µL of the fresh broth of each strain was used for inoculating 2 ml LB medium, or LB medium containing glucose (0, 2, 5, 10 and 20 g/L)or H2O2 (0, 0.2, 0.5, 1.0, 2.0 and 4.0 mM) in each well of Multiwell (24-well) plates, then cultured at 28oC for 48 h to allow float biofilms formation.