One problem facing Louisiana’s oyster industry is disease. The major culprits are the protozoans Perkinsusmarinus (Dermo) and Haplosporidium nelsoni (MSX). In the Gulf of Mexico, it is estimated that Dermo infection kills more than half the adult oyster population. Dermo and MSX have both been significant factors in the recent collapse of the oyster fishery in Chesapeake Bay. The transfer of human pathogens, such as Vibrio vulnificus and V. cholera, from oysters to humans has become a serious concern as well.
Transgenic technology may offer solutions to these problems. One focus of transgenic research at the LSU Agricultural Center
is use of reporter genes. These genes produce easily recognizable changes upon successful transfer and subsequent expression. We used a gene known as green fluorescent protein, isolated from a jellyfish, as a reporter. Oysters successfully expressing this gene produce a protein that will emit a bright green when exposed to fluorescent light. We have developed techniques for gene transfer in oyster gametes and embryos and have observed expression of green fluorescent protein in oyster larvae. We also have delivered this gene and observed expression of green fluorescence in the blood cells of adult oysters. Positive results for gene transfer with this reporter gene indicate that our techniques are effective and allow for improvement of gene transfer efficiency. Other genes of interest can be transferred with these techniques to improve disease resistance in oysters.
Research at the LSU Ag Center, conducted with support from the Louisiana Sea Grant Program, has identified proteins, known as lytic peptides, that are toxic to Dermo and Vibrio vulnifcus. In our laboratory, we have cloned genes for the lytic peptide cecropin B as well as the synthetic lytic peptide phor 21. These genes are used also in transgenic modification of channel catfish for increased disease resistance (see page 14). Delivery of genes such as these may lead to the production of an oyster capable of eliminating pathogens.
To prevent the accidental release of genetically modified organisms, we have developed techniques for working with oysters in a completely controlled environment using artificial seawater at some distance from the coast. Adult oysters are good candidates for transgenic research because they do not move and thus are easily monitored. This research is part of a comprehensive program focusing on problems facing the oyster industry.
Other research includes oyster chromosomes and physical genome mapping, sterilization and ploidy manipulation, hatchery technology, cryopreservation, artificial spawning, recirculating system techniques, cellculture, cryopreservation of gametes and larvae, pathogen biology, and oyster immune system function and defense mechanisms. Through our research, the potential exists for commercial production of sterile, genetically modified oysters for improved culture. Acknowledgments
Personnel involved in oyster gene transfer research include Philip Cheng, Jerome La Peyre, Karen McDonough, Amy Nickens, Brandye Smith and Quiyang Zhang.
John T. Buchanan, Doctoral Candidate, Department of Oceanography and Coastal Sciences; Terrence R. Tiersch, Professor, Aquaculture Research Station; and Richard K. Cooper, Associate Professor, Department of Veterinary Microbiology and Parasitology, LSU Agricultural Center, Baton Rouge, La.
(This article was published in the fall 1999 issue of Louisiana Agriculture.)