Mortality of marine picoplankton: viral infection, protistan grazing, bacterial cell defence interactions

The oceans play a major role in determining the world's climate. In part this is due to the production of oxygen and the consumption of carbon dioxide by small photosynthetic plants called phytoplankton. In the large central regions of the oceans, away from the coasts, very small unicellular cyanobacteria are the most numerous part of the phytoplankton. These cyanobacteria are continually growing and dividing, but they are also continuously being consumed. There are two major processes that contribute to the consumption of these cells. Firstly, they can be infected and killed by viruses and secondly they can be used as food by small single celled grazing animals called protists. It is the interaction between these two processes of mortality, together with the defence mechanisms that the cyanobacteria have developed, which are the focus of this research project. We would like to find out whether these cyanobacteria have specific structures on their surfaces that make them unattractive as food for the grazers. It is also possible that viruses alter the cells that they have infected to make them unattractive as food otherwise the virus would also get eaten. In most parts of the oceans there aren't enough nutrients for the cyanobacteria and it is important to find out how starvation affects their susceptibility to being grazed and infected by viruses.