Examination of shrimp exoskeleton for protective exudate in response to high bacterial concentrations.

Abstract

Our lab has been studying mechanisms by which a marine shrimp, Sicyonia ingentis , fights infection. In their natural habitat (off shore of Palos Verdes in 65 fathoms of water), these benthic animals are exposed to bacteria in the water and sediment. The exoskeleton serves as the primary barrier against bacterial infection, but I am curious as to whether it is purely mechanical or are protective chemicals secreted as well? Research has shown that when the horseshoe crab, Limulus , is exposed to high concentrations of bacteria, an antibacterial compound is secreted on top of the chitinous armor in sufficient amounts that it can be scraped off the surface and tested. In order to determine if this is also true for the shrimp, I used light as well as scanning and transmission electron microscopy to determine if there are any pores in the exoskeleton through which products could be secreted on the surface of the exoskeleton. Second, I determined the concentrations of two species of bacteria which cause death in S. ingentis . These bacteria, Vibrio harveyi and V. parahemolyticus , are known to cause mortality in related penaeid shrimp in aquaculture settings. I then immersed the shrimp in lethal concentrations of these bacteria for 24 hours and examined the surface of the exoskeleton and scraped it for exudate. My results suggest that there are two types of pores that extend from the epidermal layer into the exoskeleton. however, under the conditions tested, no obvious exudate was produced in response to the bacterial incubations as they are in Limulus .