Phytoplankton are often considered as drifters that are at the mercy of oceanic currents. However, many phytoplankton species are motile and can exhibit motile responses to light, temperature and nutrients. The prevalence of motility as a trait (e.g. >50% of Baltic Sea phytoplankton species were classed as motile) suggests that this ability is of major ecological significance, with evidence for important roles both at the microscale (e.g. exploiting heterogeneous nutrient patches) and the mesoscale (e.g. vertical migration or formation of thin layers). However, the many aspects of phytoplankton motility remain poorly understood, making it difficult to understand the wider contribution of this trait to phytoplankton physiology and ecology.
This project will address the following major questions:
1) How do abundant phytoplankton groups with distinct physiologies (e.g. haptophytes, cryptophytes and dinoflagellates) differ in their motile responses to light, temperature and nutrients?
2) Can microbially-derived organic nutrients act as chemoattractants for marine phytoplankton?
3) How are these motile responses influenced by physiological status (e.g. nutrient limitation, availability of light)?
4) What cellular mechanisms do phytoplankton use to integrate inputs from multiple stimuli to coordinate motile responses (e.g. molecular coordination of phototaxis and chemotaxis)?
- Phytoplankton cultures. The project will examine a range of motile phytoplankton species obtained from the Plymouth Culture Collection. This will include dinoflagellates (e.g Kryptoperidinium), cryptophytes (e.g. Guillardia) and haptophytes (e.g. Pavlova), representing diverse eukaryote taxa.
- Video microscopy. Swimming cells will be placed in a custom-built microfluidic chamber that will allow them to be exposed to gradients of chemoattractants whilst being imaged by light microscopy. Image analysis software will be used to track individual cells, to assess the speed and direction of movement.
- Organic nutrients. Whilst there is some evidence that phytoplankton exhibit chemotaxis towards inorganic nutrients (e.g. nitrate, phosphate), the role of organic sources of nutrients as chemoattractants has not been explored in detail. As many motile phytoplankton species are also mixotrophic (i.e. can photosynthesise and also assimilate organic nutrients), the project will examine whether the cells swim towards organic nutrients and how this interacts with the physiological status of the cell (e.g. by measuring rates of photosynthesis and respiration).
- Comparative genomics. Representative genomes and transcriptomes from each lineage will be analysed for molecular mechanisms associated with motility (e.g. photoreceptors) to determine whether major differences are present between phytoplankton taxa in sensory components that mediate motile responses.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the Marine Biological Association. Specific training will include:
- Phytoplankton culturing techniques. The student will be trained in the culturing of marine phytoplankton, including the design and implementation of nutrient limitation experiments.
- Live cell microscopy. Training will be provided in techniques for live imaging of phytoplankton motility using video microscopy and in the image processing techniques required for tracking of individual cells.
- Physiological analyses. Full training will be provided in methods to measure phytoplankton physiology (photosynthesis, respiration, cell morphology).
- Comparative genomics. The project will include training in molecular genetic approaches, including PCR-based cloning and bioinformatics (e.g. sequence similarity searches and phylogenetic analyses) to enable comparison of the gene content of different lineages.
Please see https://inspire-dtp.ac.uk/how-apply for details.
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