Projects

Viruses are important elements of marine pelagic ecosystems. They actively participate in marine microbial communities through infections of bacteria and archaea and phytoplankton. The principal effect of viral infection of phytoplankton is the so-called 'viral shunt', whereby the particulate organic matter in the form of living cells as well as cell debris is transformed into the dissolved form, providing a substrate for heterotrophic prokaryotes. This has profound effects on the biological carbon pump (BCP) that are not straightforward, however. By returning organic matter that has accumulated in primary producers back to its dissolved form it cuts the transport of carbon through the trophic chain, while simultaneously enabling further phytoplankton growth in the photic zone.

The majority of studied marine viruses are prokaryotic. Viruses infecting eukaryotic phytoplankton are far less known, and diatom viruses, one of the most abundant and diverse phytoplankton groups, were first described only in 2004. To date, roughly 20 different diatom viruses infecting 7 different genera have been described and characterized. They are all small, around 30nm big, and host either ssRNA or ssDNA genomes. The impact of viral infection on diatom populations can be substantial and can match that of zooplankton grazing in terms of biomass loss. However, the lack of data and research prevents the integration of viral lysis into phytoplankton community structure and function studies and the subsequent generation of robust carbon and production models. There is thus an urgent need to expand the known universe of diatom viruses, particularly for keystone taxa. Diatoms from the Pseudo-nitzschia genus are globally spread, bloom-forming, and can cause disturbances in food safety and ecosystem health due to the production of the neurotoxin domoic acid. Viruses infecting these diatoms have been so far hypothesized from cross-infection studies with mixed viral communities isolated from natural samples and from a preliminary investigation conducted by me where a strong indication of viral presence was recorded by transmission electron microscopy (TEM) in a culture of Pseudo-nitzschia calliantha."