BACTERIAL CLEARANCE IN PACIFIC WHITE SHRIMP, LITOPENAEUS VANNAMEI, AND THE EFFECTS OF HYPOXIA AND HYPERCAPNIC HYPOXIA

Joseph Edward Burgents, M.S.
Grice Marine Laboratory, College of Charleston, SC

ABSTRACT:  Although numerous mechanisms of immune defense have been described in crustaceans, the coordination of these mechanisms in response to pathogen challenge, including the tissue distribution and fate of live bacteria introduced into the host, remain unclear.  While the resistance of shrimp to bacterial pathogens is known to decrease in hypoxic and hypercapnic hypoxic water, the specific effects of these variables on the immune system is unknown.  Therefore, the objectives of the present thesis were two-fold. The first involved determining the main sites of localization and killing of bacteria introduced into the penaeid shrimp Litopenaeus vannamei, while the second involved determining the effects, if any, of hypoxia and hypercapnic hypoxia on the observed tissue distribution and killing of the injected pathogen. L. vannamei were injected with a sub-lethal dose of a pathogenic strain of Vibrio campbellii expressing green fluorescent protein and resistance to kanamycin.  Real-time PCR and selective plating were utilized to quantify the number of intact and culturable V. campbellii, respectively, in selected tissues.  The number of intact bacteria was used to determine the sites of bacterial accumulation, while the percentage of culturable bacteria, a measure of bacteriostatic activity, was used as an indicator of bacterial recognition and killing.  The greatest accumulation of intact V. campbellii as well as the lowest percentage of culturable bacteria was observed in the lymphoid organ.  The lymphoid organ was also the only tissue to contain a lower percentage of culturable bacteria than the hemolymph.  Hypercapnic hypoxia, and to a lesser extent hypoxia, shifted the overall distribution of V. campbellii from the lymphoid organ to the hepatopancreas and the gill.  Both hypoxia and hypercapnic hypoxia also resulted in an increase in the percentage of culturable V. campbellii recovered from the tissues.  These data suggest that the lymphoid organ, specific to penaeid shrimp, is the main site of bacterial uptake and killing, and that hypoxia and hypercapnic hypoxia decrease the resistance of shrimp to bacterial pathogens by decreasing the uptake of bacteria in the lymphoid organ as well as the systemic killing of bacteria.

Published:
Burgents, J.E., Burnett, L.E., and Burnett, K.G.  In press.  Localization and bacteriostasis of Vibrio introduced into the Pacific white shrimp, Litopenaeus vannamei. Devel. Comp. Immunol.
Burgents, J.E., Burnett, K.G. and Burnett, L.E.  In preparation. Hypoxia and hypercapnic hypoxia affect the localization and bacteriostasis of Vibrio in Litopenaeus vannamei.