Bivalve mollusks are among the most important members of benthic communities for their environmental impacts and commercial value. Infectious diseases have caused severe mortalities in bivalves such as the Eastern oyster, leading to significant alterations of ecosystem health. For most bivalve diseases, however, little is known about the dynamics of pathogen transmission, including basic information such as the routes and the mechanisms of infection or the factors that facilitate or inhibit the entry of pathogens into their hosts. Interestingly, recent studies demonstrated that pathogens (namely Perkinsus marinus the causative agent of Dermo disease in oysters) can subvert host defense factors (e.g. galectin) to gain entry in oyster blood cells and initiate infections. This collaborative effort will unite the expertise and facilities of specialists from Stony Brook University and the University of Maryland, providing a synergistic approach to determine how infectious agents hijack host defense factors associated with pallial tissues (mantle, gills) to initiate infections in the Eastern oyster. These studies on cellular and molecular host-pathogen interactions will address long-standing questions regarding mechanism(s) by which marine microbes colonize and invade bivalves. This new information is urgently needed to target future investigations to innovative strategies for disease mitigation. Beyond the specific case of oyster diseases, this project would have a fundamental impact on how scientists view initial encounters between microbes and their marine invertebrate hosts, and has the potential to lead to the development of new research approaches. From the educational standpoint, a primary objective of this project is the multidisciplinary training of graduate, undergraduate, and high school students and teachers, including underrepresented minorities, in the pathology and immunology of marine organisms. The products from research and educational activities will be disseminated by scientific electronic and printed media, including graduate dissertations and teaching modules for the classroom, as well as publications in shellfish trade magazines and fact sheets directed at stakeholders and the general public.
Bivalve mollusks are among the most important members of benthic communities for their environmental impacts and commercial value. Infectious diseases have caused severe mortalities in these animals leading to significant alterations of ecosystem health. For most bivalve diseases, however, little is known about the dynamics of pathogen transmission, including basic information such as the routes and the mechanisms of infection or the factors that facilitate or inhibit the entry of pathogens into their hosts. This project focused on early interactions between the devastating pathogen Perkinsus marinus (causative agent of Dermo disease in oysters) and the eastern oyster Crassostrea virginica. This pathogen is the main cause of oyster mortalities along the Atlantic and the Gulf coasts of the US. Experiments were designed to evaluate the mechanisms of entry of the parasite into host tissues, and to assess the role of mucosal immune factors from susceptible and resistant oysters in facilitating or, alternatively, inhibiting host colonization and invasion. Results showed that the parasite does not need to be ingested to initiate infection as initially thought. Rather, the parasite was shown to infect oyster mantle during rejection of parasite cells as pseudofeces and before reaching the mouth. Results also showed that the parasite uses mucosal secretions covering mantle tissues as a cue for the activation of virulence processes leading to tissue invasion and oyster mortalities. In contrast, mucosal secretions from resistant oysters were inhibitory and reduced parasite growth suggesting that P. marinus host specificity starts at the mucosal barrier. Investigations also revealed that oyster blood cells (hemocytes) interacts with P. marinus but are not capable of degrading parasite cells. Rather, the parasite may have evolved to manipulate hemocytes from susceptible oysters, facilitate the migration of infected blood cells and enhance host tissue invasion. Furthermore, several carbohydrate-binding proteins were identified in oyster tissues and body fluids including some that specifically recognize P. marinus cells. Overall, findings from this project unraveled the fine mechanisms of P. marinus infection in oysters as well as the host innate immune responses. This new information is essential for the development of innovative disease mitigation strategies. In parallel, the project generated a large set of data on oyster mucosal immune factors that will be highly relevant to researchers investigating early host-microbe interactions (parasitic, commensal, or mutualistic) in lower invertebrates. Further, the studies have shown the potential of the oyster-P. marinus interactions as a model system for gaining insight into the basic infection mechanisms of protozoan parasites of agricultural or medical relevance. Members of the research team at Stony Brook University and the University of Maryland also used this project as a framework for the training of undergraduate and graduate students and several postdoctoral researchers on state-of-the-art approaches and techniques in areas ranging from biochemistry to molecular and cell biology, and quantitative microscopy. The project also produced educational material (including a postcard series) that describes the importance and the sensitivity of shellfish resources. Altogether, the scientific information generated by the project and the educational initiatives contribute to the promotion of science and to the protection and enhancement of natural resources.
