MOLECULAR AND ECOLOGICAL ASPECTS OF THE INTERACTIONS BETWEEN <i>AUREOCOCCUS ANOPHAGEFFERENS</i> AND ITS GIANT VIRUS

Viruses are increasingly being recognized as an important biotic component of all ecosystems including agents that control the rapid ecological events that are harmful algal blooms (HABS). Aureococcus anophagefferens is a pelagophyte which causes recurrent ecosystem devastating brown tide blooms along the east coast of the USA and has recently spread to China and South Africa. It has been suggested that a large virus (AaV) is possibly an important agent for demise of brown tide blooms. This observation is consistent with the recognition of a number of other giant viruses modulating algal blooms in marine systems. In this dissertation, we investigated both the molecular underpinnings of Aureococcus-AaV interactions and the dynamics of AaV and the associated viral community in situ. We determined the genome sequence and phylogenetic history of AaV using high throughput sequencing approach and revealed it’s intertwined evolutionary history with the host and other organisms. Building upon the available genome of AaV and its host, we took an RNA-seq approach to provide insights on the physiological state of the AaV-infected Aureococcus ‘virocell’ that is geared towards virus production. In situ activity of AaV was detected by targeted amplicon and high throughput community RNA sequencing (metatranscriptomics) from Quantuck Bay, NY, a site with recurrent brown tide blooms. AaV and associated giant algal viruses in the Mimiviridae clade were found to respond to environmental changes, indicating that this newly recognized phylogenetic group is an important contributor to the eukaryotic phytoplankton dynamics. Analyzing time series metatranscriptomics from two distinct coastal sites recovered diverse viruses infecting microeukaryotes (including AaV) as part of interacting networks of viruses and microeukaryotes. Results from these studies testify AaV as an important factor for brown tide bloom demise, reveals the molecular underpinnings of AaV-host interactions and establishes the ecological relevance of Mimivirus-like algal viruses. We also provide foundation for using metatranscriptomics as an important tool in marine virus ecology – capable of recovering associations among coexisting marine microeukaryotes and viruses.