Title: Estuarine virioplankton: Viromics, biogeography, and viral populations

Speaker: Mengqi Sun (Ph.D. Candidate, UMCES-IMET)

Abstract: 
Viruses are ubiquitous and abundant in the oceans, influencing the biological abundance, genetic exchange and biogeochemical cycles in marine ecosystems. Viral metagenomes (viromes) have been investigated extensively via several large-scale ocean sequencing projects. Estuaries are highly productive aquatic environments featuring dynamic environmental gradients, providing a vital connection between marine and terrestrial ecosystems. However, there has not been any systematic viromic studies in estuaries.

Here, we investigated viromes of the Delaware and Chesapeake Bay, two Mid-Atlantic estuaries. This is the first systematic study of the spatial and temporal variation of the viral community in estuarine habitats using deep metagenomics, and also one of the highest quality viromic datasets to date. We refer to this viromic dataset as the Delmarva Estuarine Virome (DEV).

Unknown viruses represented the vast majority of the dominant populations, while the composition of known viruses, such as pelagiphage and cyanophage, appeared to be relatively consistent across a wide range of salinity gradient and in different seasons. Two in-depth investigations into a rare virus group (N4-like virus) and an abundant virus group (pelagiphages) were conducted. N4-like viruses were confirmed to be rare in the estuary, and found to be more abundant in colder environments. Pelagiphage (viruses infecting SAR11 bacteria) abundance was found to have no correlation with environmental factors, despite their association with oceanic environments. The methods used to study these groups indicate that more caution should be used when evaluating the relative abundance of rare viruses, compared to abundant viruses.

The difference of viral community between the Delaware Bay and Chesapeake Bay is significantly more pronounced than the difference caused by temperature or salinity, indicating strong local profiles caused by the unique ecology of each estuary. Highly abundant viruses in both estuaries have close hits to viral sequences derived from the marine single cell genomes or long read single molecule sequencing, suggesting that important viruses are still waiting to be discovered in the estuarine environment.

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