DANTZLER, A.S.*; BURNETT, K.G.; BURNETT, L.E.: Effects of Hypercapnic Hypoxia and Respiratory Burst Inhibition on the Bactericidal Activity of Hemocytes from the Penaeid Shrimp Litopenaeus vannamei

The high densities of shrimp found in aquaculture ponds cause dissolved oxygen levels to fall below 30% air saturation. Low oxygen is usually accompanied by increased carbon dioxide and low pH. Previous studies from our lab demonstrated that these conditions of hypercapnic hypoxia decreased the resistance of aquacultured shrimp Litopenaeus vannamei to infection with the opportunistic bacterial pathogen Vibrio parahaemolyticus. Reactive Oxygen Species (ROS) serve an important role in bacterial killing by vertebrate macrophages and granulocytes, but their role in the killing activity of invertebrate hemocytes remains unclear. Hypercapnic hypoxia decreased the bactericidal activity and ROS production by phagocytes from the teleost fish Fundulus heteroclitus , and the ROS production by hemocytes of the Eastern oyster, Crassostrea virginica . The current study focuses on the changes in bactericidal activity of hemocytes from the white shrimp L. vannamei under conditions of hypercapnic hypoxia and the involvement of ROS in this bacterial killing. Hemocytes isolated into a buffer of 2% artificial sea water with 0.1M glucose and buffered with 12 mM HEPES, pH 7.6, maintained viability above 90% for over four hours when held in siliconized microcentrifuge tubes. Shrimp hemocytes killed 22—84% of co-cultured bacteria using bacteria to hemocyte ratios from 10:1 to 1:10, as measured using a tetrazolium dye-based bacterial killing assay. These results are being verified by direct counts of colony forming units on TCBS agar. The effects of hypercapnic hypoxia and the NADPH-oxidase inhibitor DPI on this killing activity are also currently under investigation. (USDA CSREES 99-35204-8555)