Modulated heat shock protein expression during pathogenic Vibrio alginolyticus stress of sea bream

The effects of infective Vibrio alginolyticus and its extracellular product (ECP) on host fish function are not well understood. In this study a partial biochemical characterization of the ECP from an infective strain of V alginolyticus isolated from diseased silver sea bream Sparus sarba was achieved and the effects of live V. alginolyticus and ECP on hepatic heat shock protein (hsp) expression was compared. The ECP fraction was found to contain several hydrolytic enzymes including both haemolytic and proteolytic activities. Intramuscular administration of ECP to sea bream resulted in vibriosis with similar pathological signs as those observed with live V. alginolyticus administration. Using quantitative immunoassays we assessed the levels of the major hsp families, hsp90, hsp70 and hsp60, in hepatic tissue of diseased sea bream between 12 and 48 h post-infection. Throughout the infective period, live V alginolyticus did not alter hsp90 whereas ECP significantly reduced hepatic hsp90 during the late stages of acute infection. The levels of hsp70 were found to be rapidly and drastically increased with both live V. alginolyticus and ECP. The transcript levels of both gene members of the hsp70 family (hsc70 and hsp70) were significantly increased with both live V alginolyticus and ECP. The levels of hsp60 remained unchanged with both live V alginolyticus and ECP. The data presented in this study is the first report describing an effect of both live V alginolytus and ECP on hsp expression in diseased fish.