Rhamnolipid quantification

P. aeruginosa rhamnolipid production was quantified utilizing a drop collapse assay, as previously described [33]. Briefly, clarified supernatants from overnight cultures of P. aeruginosa strains were serially diluted (1:1) with deionized water plus 0.005% crystal violet for visualization. Twenty-five microliters of aliquots of each dilution were spotted on to the underside of a petri dish plate and tilted to a 90° angle. Surfactant scores represent the reciprocal of the highest dilution at which a collapsed drop migrated down the surface of the plate.