Polysaccharide production and biofilm formation by Pseudomonas fluorescens: effects of pH and surface material

摘要

Although the synthesis of extracellular polysaccharides hasbeen recognized in certain bacterial cultures since a long timeago, its role in bacterial adhesion is still subject to some debate.Several fermentation batch cultures were performed atdifferent conditions of pH (pH 7 and pH 8, maintained withNaOH and HCl, pH 7 phosphate buffer, and without pH control)in order to study the relation between the production ofextracellular polysaccharides and biofilm formation onpolymeric slides suspended in the culture medium. Thepolymers used were: polystyrene, polypropylene, low and highdensity polyethylene and polyvinylchloride.The maximum amount of exopolysaccharides in theculture medium occurs at pH 7 (controlled with NaOH and HCl),although the thicker biofilms are formed when there is no pHcontrol. It should be noted that the NaOH can dissolve part ofthe capsular polysaccharides and this may bias thedetermination of polysaccharides in suspension.The biofilms were analysed by Scanning ElectronMicroscopy (SEM) and by Wavelength Dispersion Spectroscopy(WDS). Biofilm morphology seems to be much more dependenton the type of substrata than on the pH of the medium: fordifferent pH values, a polymeric network can be more clearlyobserved on biofilms formed on all surfaces except thepolyvinylchloride one.