Excellence in Research: Microbiome of the Eastern Oyster (Crassostrea virginica) and its denitrification potential in benthic systems

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Oyster populations have declined worldwide, but reef restoration efforts and expanding aquaculture operations are helping to meet consumer demands. In addition to their food value, oysters improve water quality via their filter feeding mechanism, thus cleaning the surrounding water, removing organic matter than can cause low-oxygen 'dead zones', and assisting in mitigation of nutrients like nitrogen and phosphorus from terrestrial runoff. Oysters contain microbial communities that may include harmful as well as beneficial bacteria, involved in nutrient cycling and other ecosystem services. The structure and function of these microbial communities are poorly understood, especially in warm temperate and tropical water habitats. Therefore, obtaining a better assessment of what microbes are present, and their environmental functions, in wild and cultured oysters under a variety of growth conditions are the focus of this work. In particular, the research team will investigate the microbiomes associated with the conversion of dissolved nitrogen into nitrogen gas. This process removes nitrogen that can act as a fertilizer for undesirable algal blooms in coastal waters. The investigators' hypothesis is that oyster-associated microorganisms are responsible for significant nitrogen losses within the estuarine waters, improving water quality and mitigating algal blooms and fish kills. This project will also enhance research and training activities at two historically black colleges/universities, and further the education and training of minority students in STEM disciplines. A comprehensive understanding of the oyster microbiome will improve understanding of nutrient dynamics in coastal systems and help improve strategies for managing coastal water quality and reducing nutrient pollution.Oysters and their associated microbiomes provide significant environmental benefits, including removal of nitrogen, a major cause of coastal and estuarine eutrophication. However, the presence, abundance, metabolic activity and ecological significance of microbial endosymbionts within oysters, especially in warm temperate and tropical waters, remain poorly understood. Much of the oyster microbiome consists of taxonomically unresolved and potentially novel microorganisms. Filling this knowledge gap is critical because oyster aquaculture and restoration of oyster reefs is greatly expanding in the Gulf of Mexico and south Atlantic coasts. Towards this end, the research team will investigate the microbiomes of wild and cultured oysters grown under different nutrient, temperature and salinity regimes. In addition to the microbiome community composition and potential identification of novel microbes, they will focus on microbes associated with biogeochemical cycling, particularly denitrification. One major hypothesis is that oyster microbiomes provide a significant ecosystem service of nitrogen removal in estuarine systems. They will measure dissolved and particulate nitrogen species, rates of transformations and denitrification gene abundances (nosZI and nosZII), to better understand the oyster microbiome's role in N dynamics. Several emergent "omics" techniques will be utilized by a team of ecologists, microbiologists, bioinformaticians and biogeochemists from two HBCUs, thus supporting the development and expansion of research capacity at these institutions. The project also includes a significant education component, including funding for students and a postdoctoral fellow. Better understanding of the structure and function of oyster microbiomes will advance knowledge of estuarine ecology and may provide improved strategies for managing coastal water quality. This award was co-funded by the Integrative Ecological Physiology Program in the the Division of Integrative Organismal Systems and the Historically Black Colleges and Universities Undergraduate Program in the Division of Human Resource Development.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.