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

Abstract

Although the synthesis of extracellular polysaccharides was first recognized in certain bacterial cultures a long time ago, its role in bacterial adhesion is still subject to some debate.

Several fermentation batch cultures were performed under different conditions of pH (pH 7, maintained with NaOH and HCl; pH 7 in phosphate buffer, and without pH control) in order to study the relation between the production of extracellular polysaccharides and biofilm formation on polymeric slides suspended in the culture medium. The polymers used were polystyrene, polypropylene, polyethylene and poly(vinyl chloride).

The maximum amount of exopolysaccharides in the culture medium occurs at pH 7, although slightly thicker biofilms seem to be formed when there is no pH control.

The biofilms were analysed by scanning electron microscopy and by wavelength dispersion spectroscopy. Biofilm morphology seems to be much more dependent on the type of substratium than on the pH of the medium; for different pH values, a polymeric network can be more clearly observed on biofilms formed on all surfaces except poly(vinyl chloride).