Microbiology and Parasitology Laboratory

Two of the major diseases that impact the oyster production in North America are “Dermo” disease caused by Perkinsus marinus and “MSX” (multinucleated sphere X) disease caused by Haplosporidium nelsoni. These protozoan parasites have devastated natural and farmed oyster populations in the United States, significantly affecting the shellfish industry and the estuarine environment. In some cases, the gradual expansion of their geographic distribution has been associated with global warming and shellfish trade. The Perkinsozoa occupies a key position at the base of the dinoflagellate branch, close to its divergence from the Apicomplexa, a clade that includes parasitic Protista of human and veterinary relevance. Thus, as a taxon that has also evolved toward parasitism, the Perkinsozoa has attracted the attention of biologists interested in understanding adaptations (e.g., parasitism), structural evolution (e.g., plastid and plastid targeting), and identifying new targets for intervention. Vaccination of oysters is not an option, since as invertebrates, oysters lack adaptive immunity; consequently, most intervention strategies have focused on management of the resource with little success. Currently, I am using a combination of molecular tools to address a range of questions about host-parasite interactions, the genetic basis of resistance against infectious diseases, identification of new targets for intervention, and applications of marine protozoan parasites to biomedicine and biotechnology.

Scope of Work

  • Dissecting the pathways linked to a relic plastid in Perkinsus may lead to potential targets for the development of chemotherapeutic drugs or oysters genetically modified for disease resistance.
  • Identifying algae-produced compounds that inhibit the proliferation of marine protozoan parasites affecting oysters.
  • Characterizing and evaluating the iron transporters Nram li in C. virginica as resistance markers to be used for selective breeding in oyster farming and environmental restoration.
  • Developing methodologies for using marine organisms for the production of recombinant proteins of medical relevance and eventually as a platform for vaccine delivery.

Current Projects (and Funding Sources)

  • A heterologous expression system for Apicomplexa genes. NIH (R21)
  • Role of the oyster transporter CvNram li in the resistance of mollusks to infectious diseases. (Bigelow Laboratory, NSF)
  • Development of an in vitro methodology for culturing Haplosporidium nelsoni: a tool for identifying novel intervention strategies against MSX disease. (Bigelow Laboratory)
  • Screening of the Provasoli- Guillard National Center for Marine Algae and Microbiota algae collection for active compounds against protozoan pathogens causing oyster diseases. (Bigelow Laboratory)

Recent Findings and Fieldwork

  • Mining of the Perkinsus genome reveals mounting evidence in support of the presence of a relic plastid in P. marinus raising intriguing questions regarding the potential functions and unique adaptation of the putative plastid and/or plastid genes in the Perkinsozoa.
  • The validation of the Perkinsus marinus ATP-based viability assay underscores its value for the identification of novel leader compounds against Perkinsus species, and most importantly, for the closely-related apicomplexan parasites.
  • Human consumption of Perkinsus -infected oysters is likely to occur, but to our knowledge it has not been investigated in mammals whether P. marinus induces gut pathology or whether oral immunization occurs upon consumption. Oral feeding of mice with live P. marinus did not induce pathology as manifested by histological examination but induces a strong humoral response.

Future Directions and Priorities

  • Although a considerable body of knowledge has been developed about intracellular parasites affecting mollusks in order to understand and control parasitic diseases, a defined marker for disease resistance that would be critical to selective mollusk breeding programs still remains to be identified and validated.
  • Perkinsus trophozoites are taken u li by bivalve hemocytes, circulating cells that are involved in shell formation and repair, transport of nutrients, and defense. Consequently, by disrupting the hemocytes, Perkinsus infections impact most bivalve processes. Once inside the host, trophozoites are confined within the hemocyte or in intracellular spaces. I am interested in studying the role of programed cell death (PCD), a strategy to regulate numbers under non-favorable density dependent conditions to benefit survivors.
  • During the last decade, we have witnessed the sequencing of genomes of the most relevant human parasites. With the mining of these genomes and the identification of genes of interest, the need for heterologous expression systems as fundamental tools for protein function/ structure studies, antigen production, screening and profiling of candidate drugs, and understanding their action mechanisms has become evident.
  • Heterologous systems have been used with varying degrees of success. Perkinsus marinus and other marine protozoans may constitute a useful alternative when available systems perform sub-optimally for production and display of apicomplexan antigens and for use as a delivery platform for human parasite vaccines.