Bacteria Host in Squid Samples

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Nyholm and Mcfall-Ngai. 1998. Sampling the Light-Organ Microenvironment of Euprymna scolopes: Description of a Population of Host Cells in Association with the Bacterial Symbiont Vibrio fisceri. Biol. Bull. 195: 89-97 Upon collecting a species of squid, Euprymna scolopes, from the coast of Oahu, Hawaii, it was revealed that a light organ contained near its mandible is host to a bioluminescent bacteria, Vibrio fisceri. These light-organ crypts have lateral pores that expel a dense matrix consisting of live and dead host cells with the bacterial cells often adhered to their surface, in response to exposure to a light cue, which in its natural seawater habitat would occur every day at dawn. This study (Nyholm and Mcfall-Ngai, 1998), examines this diel rhythm in terms of the cycle and the contents of the matrix in the light-organ of E. scolopes, “including aspects of nutrient exchange, host immune response, and the control of symbiont number”(Nyholm and Mcfall-Ngai, 1998). Under a natural 12 hour dark 12 hour light cycle, the animals were anesthetized in ethanol and the light-organ was exposed to a light source and after staining the host cells, the exuded material was collected (lack of a light stimulus produced no venting). However, the matrix obtained from the organ was prepared for observance under scanning and transmission microscopy at different time intervals in the cycle. From this it was determined that levels of the bacteria are highest before dawn and drops to level of 5 to 10% just after venting, indicating that the purpose is removal of the bacteria from the organ. Some of the E. scolope cells in the exudate contained acidic lysosomes, and “spaces of intact light organs occasionally contained intracellular bacteria…and many of the cells appeared to be undergoing degradation”(Nyholm and Mcfall-Ngai, 1998). Along with the active cells of E. scolope, many are also dead or non-functional, in fact microscopy revealed that around half of them had compromised membranes.

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