Figure 4. Biofilm formation ability of strains M6 and 7a1 and their corresponding variants.

Cultures were grown in XVM2 medium for 48 hours in polystyrene ELISA plates at 28 ^°C. Formed biofilms at the medium/air interface were stained with 0.01% crystal violet stain. Stained biofilms were resuspended with ethanol and quantitatively estimated by optical density measurements at 595 nm. Top, middle and bottom panels show the results of three independent experiments (first, second, third; with five replicates per strain in the first experiment, and ten replicates per strain in second and third experiments). The box-and-whisker plots indicate minimum, first quartile, median, third quartile, and maximum values. Different letters indicate statistically significant differences (p < 0.05; for details see Appendix S1) among strains in each experiment.