| Summary: | 碩士 === 國立海洋大學 === 水產養殖學系 === 91 === This study investigated the virulence of Vibrio alginolyticus strain 9206 isolated from diseased white shrimp (Litopenaeus vannamei) grown at various temperature and concentration of NaCl. Virulence of the bacteria cells of V. carchariae (strain 9211) or V. paraheamolyticus (strain 9301) in white shrimp disease was also conducted for comparsion.
The LD50 values of V. alginolyticus (strain 9206), V. carchariae (strain 9211) and V. paraheamolyticus (strain 9301) in white shrimp were 7.24 104, 5.59 105 and 9.69 105 CFU / g body weight, respectively. The bacterial cells of V. alginolyticus 9206 was more virulent than the other two Vibrio species.
Vibrio alginolyticus 9206 grown at 30℃ was found more virulent in white shrimp (7g) than that grown at other different temperatures with an LD50 value of 3.12 104 CFU / g body weight. In addition, the bacterial grown at medium contained 2.5% NaCl was more virulent than that grown at other media contained different concentrations of NaCl with an LD50 value of 8.29 103 CFU / g body weight.
The extracellular products (ECP) of strain 9206 grown at 30℃ was more virulent in white shrimp (7g) than that grown at other different temperatures with an LD50 value of 0.46 µg protein / g body weight. The ECP of strain 9206 grown at medium contained 2.5% NaCl was more virulent than grown at other medium contained different concentrations of NaCl with an LD50 value of 0.24 µg protein / g body weight.
A fraction contained 34KDa protein band on SDS-PAGE exhibiting protease activity was partially purified from ECP of strain 9206 by using anion exchange columns (Hydrophobic interaction chromatography and RESOURCE-Q) on Fast Protein Liquid Chromatography (FPLC).The purified protease fraction was lethal to white shrimp.
Antiserum to the 34KDa protease was raised in a rabbit and obtained for the quantative assay using Rocket immunoelectrophoresis. The result revealed that the activity and amount protein content of protease (34KDa) in the ECP of strain 9206 was higher when grown at higher temperature or higher NaCl concentration in media tested. The ECP of strain 9206 grown at medium containing 2.5% NaCl exhibited high virulence with low protease amount indicating the possible presence of other lethal factor(s). However, further experiments are needed to prove it.
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