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Characterization Of A Bacterial Pathogen Associated With
Plague Type II: Chemotaxis And Mechanism
Of Coral Tissue Necrosis Michael F. Walker1 , Garriet W. Smith2, Laurie L. Richardson1 1Department of
Biological Sciences, Florida International University, Miami, FL 33199; 2Department
of Biology, University of South Carolina, Aiken, SC 29801 The coral disease termed plague type II
rapidly destroys coral tissue on reefs in the Florida Keys. The pathogen is a bacterium postulated to be
a new species of the genus Sphingomonas. While this pathogen has been shown to infect
coral in the laboratory and initiate the disease, virtually all of the
mechanisms of disease etiology are unknown.
Bacterial chemotaxis is a factor that could be driving the process of
coral tissue destruction, assuming a gradient of attractant is created as the
coral tissue necroses. We are
investigating the mechanism controlling the novel progression of the
pathogen-induced disease line during infection of the coral Dichocoenia stokesii, by determining the
relationships between chemotaxis, disease line progression, and coral tissue
necrosis. To date, Sphingomonas has been isolated from plague type II diseased corals
of the Florida Keys and the U.S. Virgin Islands, as determined by cluster
analysis of results of the Biolog assay.
This assay is based on carbon source utilization patterns with 95
possible carbon sources. Chemotaxis research is currently focused on two
isolates from the Florida Keys from two different plague type II outbreaks
(1995 and 1999). The chemotactic activity of the 1995 isolate is different from
that of the 1999 isolate, which may be related to an observed loss of
pathogenicity of the 1995 strain (maintained in the laboratory on marine agar).
Results to date indicate that the 1995 strain is attracted to arginine, while
negative chemotaxis is observed for lysine, proline, and glucose. The 1999
strain shows positive results for case amino acids, aspartate, lysine, proline,
and arginine(10mM), and negative results for beef extract and a lower
concentration of arginine(1mM). The results of this study will increase current
knowledge of the etiology of plague type II.
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