Researchers from the University of Georgia College of Veterinary Medicine have made an "unexpected" dual discovery that could open new avenues for treating Ichthyophthirius multifiliis, or "Ich", a devastating single-celled protozoan parasite that commonly attacks freshwater fish.
With the aid of whole-genome sequencing, researchers found that Ich harbors two apparently symbiotic intracellular bacteria: Bacteroides, which are usually found free-living, and Rickettsia, which are obligate intracellular bacteria. The two bacteria represent new species.
Five researchers from the College's Department of Infectious Diseases worked on the project in collaboration with two researchers from the Department of Microbiology and Immunology at Cornell University College of Veterinary Medicine, and a researcher from the J. Craig Venter Institute, a DNA sequencing laboratory; their initial intent was to map the genome of Ich. Their study is published in the December 2009 issue (Issue 23) of "Applied and Environmental Microbiology," with an image from the study donning the cover.
It was the presence of Rickettsia DNA sequences found in the initial genome data that provided scientists with a clue that bacteria might live inside of Ich. Intracellular bacteria have been described in free-living ciliates such as Paramecium, but never in Ich, which is an obligate parasite.
"It was unexpected; it was stunning to find bacteria in Ich. And, it came about due to the genome sequencing," said Harry W. Dickerson, a co-author who has been studying Ich at the Veterinary College for more than 20 years. Dickerson is also a member of the University of Georgia's Center for Tropical and Emerging Global Diseases, which has a focus on parasitic diseases, primarily of humans. "Ich occurs world-wide and is one of the most common protozoon pathogens of freshwater fish. It is easily recognized by most aquarists, and fish farmers often are confronted
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University of Georgia