Extraction, purification and biological activity analysis of extracellular products of Aeromonas hydrophila GYK1 strain isolated from mandarinfish(Siniperca chuatsi)

Extracellular products(ECP)of Aeromonas hydrophila (Ah) GYK1, isolated from mandarinfish, Siniperca chuatsi and other 7 strains of Ah and 1 strain of A.sobria were extracted by cellophane cover technique. Some characteristics of the ECP of GYK1 strain were analyzed. The ECP of GYK1 strain had enzyme activity of caseinase, amylase, lipase and gelatinase, but had not activity of urease. The ECP also had strong hemolytic activity. The hemolytic titer of crude ECP, with protein concentration of 365 μg·mL^-1, to erythrocyte of mandarinfish was 2¹³, to that of other two kinds of fishes and five kinds of mammals were between 2¹¹~2¹⁴.The result of SDS-PAGE showed that the band with molecular weight about 35 kDa is the common protein band of the ECP of the tested 8 Ah strains. ECP of GYK1 strain was purified and the band of 35 kDa was obtained by Hiprep^® Sephacryl S-200 high resolution chromatography. And the purified product had hemolytic activity, but was weaker than that of the crude ECP. The hemolytic titer of crude ECP to mandarinfish and mouse was 2¹³ and 2¹², while that of the purified ECP was both 2⁵.