The effect of temperature on bacteria-host interactions in the freshwater crayfish, Pacifastacus leniusculus

Water temperature is known to affect many aspects of aquatic life including immune responses and susceptibility to diseases. In this context, we studied the effect of temperature on the defense system of the freshwater crayfish Pacifastacus leniusculus. Animals were challenged with two pathogenic Gram-negative bacteria, Aeromonas hydrophila and Pseudomonas gessardii, as well as the bacterial cell wall component lipopolysaccharide (LPS) at two different temperatures, cold (6 degrees C) and room temperature (22 degrees C). The immune responses were compared by means of differences in mortality, phagocytosis, bacterial clearance, and the melanization reaction of the hemolymph at these two temperatures. We observed that crayfish survival was higher at cold temperature. The mortality rate was zero at 6 degrees C following A. hydrophila or LPS injections. Furthermore, the bacteria were completely cleared from crayfish after they had been held at 6 degrees C for more than 9 days. We also observed a strong melanization reaction of hemolymph at 22 degrees C when stimulated with LPS, as well as with bacteria. Taken together, our results suggest that the cellular immunity is more effective at low temperature in this cold-adapted animal and pathogens are efficiently removed from the body by mean of phagocytosis.