Date of Completion

Spring 5-10-2009

Thesis Advisor(s)

Spencer V. Nyholm

Honors Major

Cell Biology

Disciplines

Cell Biology | Molecular Biology | Other Animal Sciences

Abstract

The subject of our study is the Hawaiian bobtail squid, Euprymna scolopes, which is known for its model symbiotic relationship with the bioluminescent bacterium, Vibrio fischeri. The interactions between E. scolopes and V. fischeri provide an exemplary model of the biochemical and molecular dynamics of symbiosis since both members can be cultivated separately and V. fischeri can be genetically modified 1. However, in a laboratory setting, the mortality of embryonic E. scolopes can be a recurrent problem. In many of these fatalities, the egg cases display a pink-hued biofilm, and rosy pigmentation has also been noted in the deaths of several adult squid. To identify the microbial components of this biofilm, we cloned and sequenced the 16s ribosomal DNA gene from pink, culture-grown isolates from infected egg cases and adult tissues. One of the culture-grown species was identified as Phaeobacter, a genus of bacteria related to Roseobacter, a resident component of the accessory nidamental gland (ANG), an organ involved with the secretion of the jelly egg coat in squids. To establish if Phaeobacter was acting as a pathogen, we infected juvenile E. scolopes with concentrations of Phaeobacter ranging from 103 to 106 cells per milliliter of filter-sterilized sea water. Our data suggests that Phaeobacter may be a causative agent in the deaths of juvenile squids. Current molecular analyses seek to identify Phaeobacter as a resident of ANG tissue, as well as identify and obtain cultured isolates of other bacteria that may reside in the ANG. Symbiotic relationships can potentially turn pathogenic. For example, resident and normally benign bacteria of the human gastrointestinal tract, Helicobacter pylori and Escherichia coli, contribute to disease in a small segment of the human population. Hence, understanding the mechanisms whereby resident microbiota become pathogenic in the model squid E. scolopes, may have broader implications in understanding the progression of some infectious diseases.

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