How do marine virus puppets affect ocean photosynthesis?

Primary Supervisor: Professor Dave Scanlan (University of Warwick)
Secondary supervisors: Dr Richard Puxty (University of Warwick) and Dr Andrew Millard (University of Leicester)

Project overview
The oceans play a major role in determining world climate via the production of oxygen and the consumption of carbon dioxide largely by tiny, single celled organisms, the photosynthetic picoplankton. These organisms, which are numerically dominated by the cyanobacterial genera Prochlorococcus and Synechococcus can be responsible for up to 70% of CO2 fixation in some oceanic regions [1]. Marine cyanophages, viruses infecting both Synechococcus and Prochlorococcus [2], appear to be extremely abundant (up to 106 ml-1 [2]) in most aquatic ecosystems, and a key current question is to what extent viruses drive the structure and function of these marine picophytoplankton communities, and in so doing dictate the fate of fixed carbon.

Cyanophages are exceptional in that they also appear to play a direct role in CO2 fixation since they carry genes that are essential for photosynthesis [3, 4, 5]. The phage derived copies of psbA encoding core photosystem II reaction centre proteins are thought to maintain cellular photosynthetic activity during infection thus maximizing the production of progeny phage. The viral psbA gene is an example of an auxiliary metabolic gene (AMG) carried by the phage. Other AMGs include various components of the photosynthetic machinery and central carbon metabolism. Understanding how cyanophage AMG carriage is affected by the actual environment the phage inhabits is a key question that will help unlock the role and selective advantage of carrying these AMGs under specific conditions and will be facilitated by isolating phage from a research cruise transect obtained in the Atlantic Ocean.

In addition to environmental control on AMG carriage, AMG fitness landscapes may be shaped by specific hosts that each phage infects. However, our understanding of the determinants of host range are poor. In the first instance, phages must adsorb to their host using the combination of a host receptor and a phage receptor binding protein. These are likely primary genetic determinants of host range, yet we have no idea what they are! Using cutting edge genetic approaches this PhD project can also then elucidate both the phage tail fibres and host receptors and facilitate a molecular understanding of the viral-host arms race.

The project will provide excellent training in a range of molecular biological, biochemical & microbiological techniques. The student will benefit from the wide array of scientific expertise already available in the host labs.

This exciting project funded as part of a large Advanced European Research Council (ERC) grant represents a fantastic opportunity to greatly advance our understanding of lytic phage-host interactions whilst, at the same time, developing a range of research skills.


Key experimental skills involved: Cutting-edge molecular and microbiology techniques, e.g. transcriptomics, proteomics, microbial physiology and analytical photosynthetic skills e.g. PAM fluorometry.