Effects of nutrients on exopolysaccharide production and surface properties of Aeromonas salmonicida.

Extracellular polysaccharide (EPS) and capsular polysaccharide (CPS) production by Aeromonas salmonicida A450 and the influence of the capsule on cell surface properties were studied. A. salmonicida did not produce CPS or EPS when glucose, phosphate, magnesium chloride, or trace mineral components were absent from the medium. The addition of yeast extract improved capsule production. Neither EPS nor CPS formation depended on the C/N ratio, although it appeared to be influenced by the level of carbon and nitrogen in the culture. Both EPS and CPS production started at the end of the logarithmic growth phase. The amounts of EPS and CPS produced were not influenced by temperature changes between 15 and 20 degrees C and was maximal from pH 7 to 7.5. Cell surface properties were strongly influenced by capsule production; high CPS production was associated with enhanced cell hydrophilicity and autoagglutination. The effect of CPS on cell surface properties was independent of the presence of the surface protein array (A-layer).