Biofilm Exopolysaccharides

Abstract

The presence of exopolysaccharides as essential components of biofilms can be demonstrated by chemical analysis or by direct examination of the biofilm using microscopy or electron microscopy. The development of specific staining methods has revealed both the attachment of cells and the presence of microcolonies surrounded by extensive amounts of exopolysaccharide (e.g. Allison and Sutherland 1984). In such laboratory experiments of biofilm elaboration on glass surfaces, there was good correlation between the physical appearance of exopolysaccharide and the amount of carbohydrate-containing material attached to the glass. Scanning electron microscopy (SEM) studies have also revealed material thought to be polysaccharide in nature (Fig. 1). An SEM examination of bacteria attached to sand grains has revealed strands of polysaccharide or glycoprotein-like material thought to attach the cells to the solid surface (Weise and Reinheimer 1978). The strands were of varying thickness and were associated with various types of cells. However, this material cannot be chemically analysed and may also be subject to artefacts from specimen preparation. On the other hand, use has been made of ruthenium red, a dye which interacts strongly with polysaccharides and can be visualised under the transmission electron microscope. Thus, natural biofilms revealed dense populations of bacterial cells enmeshed in fibrous structures (Geesey et al. 1977). Although other reports using this technique have also indicated the presence of fibrous material presumed to be polysaccharide, the actual appearance depended on the method used for sample preparation.