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Extracellular polysaccharide (EPS) and capsular polysaccharide (CPS) production by Aeromonas sabnonicida 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°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). Aeromonas salmonicida causes fish furunculosis, an infectious disease principally of salmonid fish (16, 17). Virulent strains produce a surface protein array (A-layer) (9), which is crucial to the virulence of this organism (6) and has been found to be associated with an increase in cell surface hydrophobicity (25). Interactions between bacteria and their environment, including pathogenic phenomena, normally involve specific interactions between macromolecules found on bacterial and host cell surfaces (19). The macromolecular components of bacterial surfaces, e.g., lipopolysaccharide (LPS), protein, and exopolymers, have been shown to vary in quantity and composition with growth conditions (3). Changes in cell wall or polymer composition have a strong influence on the physicochemical properties of the cell surface, e.g., via differences in hydrophobicity (13). Recently, Garrote et al. (5) have demonstrated the production by A. salmonicida of completely cell-detached extracellular polysaccharide (EPS) and cell-bound capsular polysaccharide (CPS). Since capsular polysaccharide is found on the bacterial surface, we proposed to assess the influence of this CPS on A. salmonicida cell surface properties. The aim of our work was also to study the effects of growth medium composition and environmental conditions on the formation of exopolysaccharides (sum of EPS and CPS) byA. salmonicida. MATERIALS AND METHODS Organisms. A. salmonicida strains used in this study were

The influence of some ions in pre-growth culture medium on chromate reduction by resting cells of Agrobacterium radiobacter strain EPS-916 was investigated, The reduction was dependent on the Fe 2÷ content of the culture medium: the higher the iron content, the lower the reduction rate. The cells showed maximum chromate reduction when pre-grown in the presence of 0.243 [.tM Mg 2+, 20 [.tM C a 2+ and 3.6 ~tM Mn 2+. Chromate reduction was not affected by the addition of MgClz, CdClz, ZnCI2, MnClz, Na2SO4 (1000 ~tM), and NazMoO4 (100 gM) to the activity assays. However, activity was inhibited by the presence of NazSO4 (10 mM), NazMoO4 (200 gM) and ferric citrate.

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Aeromonas salmonicida grown in a medium with excess glucose as carbon source produces both capsular and exocellular polysaccharides. The capsular polysaccharide is composed of glucose, mannose, rhamnose, N-acetylmannosamine and mannuronic acid in the molar ratios of approximately 5:3:0.75:2:1. The extracellular polysaccharide is similarly constituted, but in the molar ratios of approximately 4.75:10.5:1.5:2:1. The capsular and exocellular polysaccharides did not cross-react with monoclonal antibodies against the A-layer or the O-antigen lipopolysaccharide.