The Role of Exopolysaccharides in Adhesion of Freshwater Bacteria

Cultures of two strains of freshwater bacterial isolates adhered readily to inert glass surfaces exposed in the growth medium. The process of microbial film formation could be followed by a new staining technique based on congo red, a dye specific for carbohydrate material. In conjunction with a chemical assay for total carbohydrate, the association of extracellular polysaccharides with attached cells was demonstrated. Under optimal growth conditions, the involvement of exopolysaccharide in the adhesion process appeared to follow the initial attachment of bacterial cells, leading to the formation of microcolonies enmeshed in polysaccharides. A non-polysaccharide-producing mutant attached to glass slides in numbers similar to the wild-type bacteria, but did not form microcolonies. Growth conditions such as glucose or Ca2+ limitation which affected polysaccharide synthesis in the wild-type prevented microcolony formation, but not cell attachment. It is proposed that exopolysaccharide production is involved in the development of the surface films, but possibly not in the initial adhesion-process. In those strains which do produce polysaccharide, the cells which attach develop into microcolonies.