A number of freshwater isolates were used for this study.Strain S6l, a Gram negative adhesive bacterium, was isolated from a local freshwater source. Copious amounts of exopolysaccharide are produced during growth, and play a role in the adhesion process. Analysis of extracellular polymer synthesized by both S6l and other freshwater isolates, revealed that sugars found to occur most frequently were glucose, galactose and mannose; acetate and pyruvate content varied with strain. No unusual components were found in any of the preparations assayed.
A new staining method was developed, allowing the involvement and association of exopolysaccharide in the attachment process to be viewed by light microscopy. Adhesion and biofilm formation was shown to occur in a sigmoidal manner, both in vitro and in situ. Microcolony development can be prevented by treatments known to affect the secondary and tertiary structure of the exopolysaccharide. However, these treatments have little effect upon cell adhesion.
Following mutagenic treatment, a non-mucoid variant of strain S6l was isolated. Trace quantities of exopolymer were produced, chemically identical to the wild type product. The adhesive properties of the non-mucoid mutant were not impaired; no significant difference in the attached cell numbers occurred compared to the wild type. Microcolony formation however, did not occur.
Continuous culture studies of strain S6l showed that changing both the dilution rate and the culture parameters could markedly influence the cell surface characteristics. Production and viscosity of exopolymers were affected by the growth rate, outer membrane proteins varying with culture temperature. At a low temperature, more variation was observed in the amounts of individual proteins than when grown under different conditions at a higher temperature.
Analysis of purified outer membrane material by affinity chromatography has revealed the presence of a glucose specific receptor, identified as a high molecular weight protein. Less specific receptors for other monosaccharides may also be present.The involvement of specific outer membrane receptors in the initial
stages of attachment was discussed and the possibility of an interrelationship between polysaccharide synthesis and the availability of receptors for adhesion was considered.