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Researchers to sequence major catfish pathogen
MISSISSIPPI STATE -- A current Mississippi State University research project has the potential to eliminate a devastating disease in channel catfish, one of the state's most economically significant agricultural products.
Dr. Mark Lawrence, an associate professor in the College of Veterinary Medicine's basic sciences department, is collaborating with researchers at the Oklahoma University Health Sciences Center and Louisiana State University to sequence the genome of a bacterial pathogen called Edwardsiella ictaluri. The effects of this disease range from slow weight gain to rapid mortalities in a pond.
"This bacteria has a chromosome with just over 2 million bases, and we're working to determine all the genes present in the chromosome and assign potential functions of those genes," Lawrence said. "We will use this information to identify how this pathogen causes disease in channel catfish. Studying the genes also will allow us to conduct large-scale screenings for a potential vaccine."
Edwardsiella ictaluri was first identified in the late 1970s and was recognized as a significant disease problem in the 1980s. The bacteria causes enteric septicemia, or ESC, in channel catfish.
"In its chronic form, ESC typically has a slower progression and causes a 'hole-in-the-head' lesion that may remain localized or progress to septicemia and death," Lawrence said.
Treatments currently available for this disease include two antibiotics, which are given in the catfish feed. Lawrence said this is not effective because one of the first signs of the disease in catfish is loss of appetite, so the affected catfish do not consume the antibiotic.
"By sequencing the pathogen, we can identify all the genes and compare them to genes from other bacterial genomes, like E. coli, Salmonella and Yersinia, that occur in humans," Lawrence said. "The chromosomes of those well-known bacterial pathogens have been sequenced. After we sequence Edwardsiella ictaluri, we can compare it to the sequence of these other diseases and see what genes are similar. We'll probably also find some things that are unique to catfish."
Work on this project began in December 2003 and is expected to be completed by the spring of 2006. Michele Williams is the post-doctoral associate conducting most of the MSU research. The research team also includes a research associate, another post-doctoral associate and a graduate student.
Lawrence is coordinating the project between the three universities involved.
"The researchers in Oklahoma University's Laboratory for Genomics and Bioinformatics are doing the high throughput sequencing phase of the sequence determination," Lawrence said. "Our group and the group at LSU's School of Veterinary Medicine will take the sequence they generate and strategically close all the gaps in the sequence, and resequence any areas that are questionable. Then, we'll go through the sequence and identify the genes and predict their functions."
Once the researchers complete the study, the results will be presented at an American Fisheries Society workshop, which is a gathering of fish disease researchers from around the country. The researchers will discuss how best to use the information.
Terry Hanson, an MSU agricultural economist specializing in aquaculture, said the potential impact of eliminating Edwardsiella is significant.
"ESC basically has two economic impacts on catfish producers. It not only kills the fish, but one of the treatments farmers use is to reduce or stop feeding during the optimal temperature for this disease. Thus, you have no feed being eaten by the fish and no growth," Hanson said. "This means they have to stay in the pond longer, and the longer fish stay in the pond, the more risk they have of dying from other disease outbreaks, being eaten by predatory birds like the double-crested cormorant, and other perils."
Leaving fish in the pond longer also prevents producers from getting new fish stocked and starting another production cycle.
Hanson said any method that would reduce the incidence of ESC would improve the overall efficiency of the catfish industry at both the hatchery and grow-out phases.
"We need to try any approaches that are available -- gene sequencing, vaccines, feed additives. This research really could revolutionize the industry and increase overall production," Hanson said. "Right now, we're getting 30 to 40 percent mortality -- not just from ESC, but other diseases, as well. But if we got rid of ESC, we might be able to increase survival by 10 to 15 percent, which would have enormous consequences."
Lawrence's research is funded by a competitive $350,000 U.S. Department of Agriculture Microbial Genome Sequencing Program grant.
Contact: Dr. Mark Lawrence, (662) 325-1195