University of Delaware Office of Public Relations The Messenger Vol. 5, No. 4/1996 'Fingerprinting' an oyster? When spring arrived in 1888, dozens of schooners burst out of local creeks and into the Delaware Bay in quest of "white gold"-the American oyster (Crassostrea virginica). In the heyday of the bay's oyster fishery, catches soared above 3 million bushels. During the next several decades, however, the oyster fishery began declining from overfishing and habitat degradation, although it remained a valuable industry. Then, in the late 1950s, the fishery was attacked by a single-celled parasite called MSX and later by another parasite, Dermo. It has never recovered. Last year, only about 32,000 bushels of oysters were landed in Delaware Bay. To revive the Mid-Atlantic oyster fishery, scientists and resource managers must find a way to combat the disease. In Sea Grant research at the UD, marine biologist Patrick Gaffney is working with a team of mid-Atlantic scientists to give oysters the weapons they need- disease-resistant genes. "If we can develop disease-resistant oysters, our hope is that they could be farmed by commercial mariculturists and be used to help replenish depleted waters in the Delaware and Chesapeake bays," Gaffney says. "While I don't think it's realistic to expect the oyster industry to ever be what it was years ago, disease-resistant oysters could help the industry regain some lost ground." MSX and Dermo are harmless to humans but lethal to local oysters. The parasites establish themselves on the oyster's gills as the animal filters food from the water and then invade its circulatory system. Many oysters die within eight weeks after becoming infected. Since both diseases thrive in warm, high- salinity waters, drought spells devastation for the oysters. To increase the oyster's resistance to disease, Gaffney and his colleagues are working on two basic strategies. One approach is to create a disease-resistant hybrid by breeding the American oyster (Crassostrea virginica) with the Pacific oyster (Crassostrea gigas), a hardy, fast-growing species with resistance to MSX and Dermo. The other approach is to explore the genetic diversity within the native American oyster, which is found from Nova Scotia to the Gulf states, to determine if any individuals in the species can resist disease and thus be used in breeding programs. In each case, Gaffney is drawing on the revolutionary tools of human genetic research to begin clearing a path through a jungle of oyster genes to the gene or genes for disease resistance. For example, using the polymerase chain reaction (PCR), a groundbreaking DNA fingerprinting technique borrowed from human genetics research, Gaffney and master's student Jeff Wakefield discovered that there are actually several genetic "types" within the American oyster-meaning that a South Carolina oyster is genetically different from a Long Island oyster and so forth-valuable information for scientists working to preserve species diversity and seek out disease-resistant lines. Gaffney is one of a growing number of biologists using PCR in marine science applications. This molecular technique, widely publicized in the forensics of the O. J. Simpson trial, enlists the enzyme DNA polymerase to select a segment of DNA taken from a subject's blood, tissue or hair and then rapidly replicate it, yielding a large, readily analyzed sample of DNA. Once PCR has been run on the subjects they wish to compare, scientists begin analyzing the differences between them, that is, the differences in sequence of the DNA subunits. While automated DNA sequencers can decode each product, Gaffney says, the time and expense are considerable. His goal is to develop faster, cheaper methods for screening genetic variation in oysters. One technique he now is using involves loading samples of PCR-amplified DNA onto an acrylicamide gel containing a gradient of a chemical denaturant. As an electrical current is applied, the DNA molecules in each sample migrate through the gel until they begin to denature (unwind), which causes migration to cease. The variations in stopping points quickly reveal how different the genetic compositions of the samples are. Using this technique and others, Gaffney can begin creating DNA markers to help scientists search among thousands of oyster genes for the handful that may confer disease resistance. "We're fortunate in the marine sciences that we can draw on the revolutionary technology of human genetics and the biomedical industry," Gaffney notes. "Yet, there are a lot of allied disciplines in which concepts and tools of molecular genetics are becoming more and more useful." Gaffney says he also believes molecular genetics will be critical to conservation efforts in the future. "As more species become endangered and become propagated artificially at zoos, understanding their genetics will become vital to preserving the species," he says. "Already in the marine realm, scientists have been working to understand the population structure of sea turtles and marine mammals. I think molecular genetics will only continue to grow as marine conservation biology develops, he says." -Tracey Bryant