Project 3: Do phytoplankton parasites affect marine water quality? A pioneering investigation with a focus on a dominant toxin-producing diatom

The hypothesis underpinning this area of research is that parasitism of phytoplankton is an under-estimated driver of marine ecosystem functioning. In a pilot study, we unveiled many unreported parasites infecting pelagic diatoms. A notable example was the toxin producing, dominant bloom forming diatom Pseudo-nitzschia, which was frequently subjected to outbreaks of an Ectrogella-like oomycete pathogen during the three consecutive years investigated. This diatom undergoes unexplained inter-annual variations in abundance and toxicity, making our observations particularly relevant to the regulatory framework of water quality monitoring in Scotland. This project is investigating experimentally and in silico the biodiversity and ecological impact of the parasites of diatoms, in particular on the abundance and toxicity of Pseudo-nitschzia sp.

Andrea Garvetto has been appointed researcher for this project which is based at the Scottish Association for Marine Science – SAMS. His research will characterise parasites of Pseudo-niztschia and other diatoms using single cell genome amplification of infected cells, followed by genetic markers extraction. This will confirm their phylogenetic position and set a basis to explore the ecology and diversity of these parasites in marine worldwide metabarcoding and metagenomic surveys, thus broadening the geographical and ecological significance of the project.

In order to better characterise oomycete parasites of Pseudo-nitzschia, Andrea collaborated with Dr. Siano at IFREMER Brest, where he has been hosted for two months. Here he has been working on the dynamics of newly described oomycete parasites of diatoms in the frame of seasonal blooms.

In remote collaboration with the Laboratoire Micro-organismes: Genomes et Environment at CNRS, the transcriptome of a freshwater chytrid-diatom system will be analysed to understand the molecular basis of eukaryotic parasitism on diatoms. To further shed light on this parasitic interaction Marine Scotland, will host Andrea in Aberdeen to investigate ultrastructural changes in the cell structure using Transmission Electron Microscopy.

Bringing Pseudo-nitzschia and its parasites into laboratory culture will also be attempted although this challenging step is not critical to the success of the project.