A comparative study of the formation of extracellular proteins by Aeromonas salmonicida at two different temperatures

Aeromonas salmonicida was grown in a supplemented 3% (w/v) tryptone soya broth medium at 10°C, a temperature at the lower end of the range over which furunculosis has been observed to occur in the field, and 25°C, the optimum temperature for growth. Similar bacterial densities in the range 2.35 × 0.05 mg dry wt/ml were achieved in the two cultures at the beginning of the stationary phase of the growth cycle, after 125 h at 10°C and 18 h at 25°C. At this point, at the higher temperature 1.5 times more exoprotein was formed, 80 × 2.8 μg/ml compared with 54 × 1.7 μg/ml. Exoprotein contained the same proportion of haemolysin at both temperatures and twice as much protease at the higher temperature. The most marked difference was in an unidentified 100 kD protein which was formed in a 10-fold greater amount at 10°C.