McNair/Gateway Scholars Program USC

Vickie Trinh


Major and Classification

Biological Sciences

Faculty Mentor

    Jed A. Fuhrman, Ph.D.


    Biological Sciences

McNair Project

Growth of Thaumarchaea MGI Enrichment Culture Under Viral Pressure, Photoinhibition and Exposure to Natural Marine Microbes

Until 1992, the domain Archaea was generalized to be prokaryotes living in extreme environments. Recent studies have revealed that archaea are also found in moderate environments, such as the Thaumarchaea Marine Group I (MGI), which are ubiquitous throughout the world's oceans and abundant in mesophilic waters. These organisms have been shown to be ammonia oxidizers using the enzyme ammonia monooxygenase (AMO) to oxidize ammonia to nitrite as a source of energy to fix carbon dioxide. Their ability to oxidize ammonia, the first and rate-limiting step in nitrification, and their abundance suggest that they are important players in the nitrogen and carbon cycles; however, the niches they fill within marine microbial communities and the environmental controls on their abundance are poorly understood. Studying Thaumarchaea MGI in culture can reveal how archaeal abundance is controlled by viral lysis, photoinhibition and interactions with other microorganisms. For example, we have found that the growth rates of a Thaumarchaeal enrichment culture, CN75, increase when viral pressures are reduced by dilution with 0.02 micrometer filtered seawater media, as indicated by the faster accumulation of nitrite. The nitrite accumulation rates of CN75 also decrease with exposure to light, which supports previous studies showing AMO sensitivity to light. Adding the enrichment culture to whole seawater and monitoring the changes in the microbial community composition will determine how the community changes in response to the presence and activity of MGI. Studying the environmental controls on Thaumarchaeal MGI abundance is fundamental to understanding their niche in the microbial community and where they are found in the natural environment.