Project highlights

  • Uncover the “genetic dark matter” responsible for maintaining buoyancy in marine phytoplankton
  • Test how abiotic and biotic stress impact buoyancy traits of marine phytoplankton
  • Translate discoveries of buoyancy traits into an better understanding of the Earth’s carbon cycle through the biological pump


Industrialisation has short-circuited the Earth’s carbon cycle; converting ~0.4 trillion tons of organic carbon back to CO2 from the burning of fossil fuels. The most rapidly cycled pool of carbon is in the Oceans. In the surface oceans, single celled microbes convert CO2 to particulate organic carbon (POC) through photosynthesis. POC can sink into the ocean interior, through the activity of the biological carbon pump (BCP), effectively storing it for hundreds of years (Figure 1A). Without the BCP, the predicted atmospheric CO2 concentration would be doubled.

We currently have a poor understanding of the processes that determine the strength of the BCP However, it is thought that buoyancy traits of surface marine phytoplankton plays a key role [1]. These organisms face a consistent challenge to fight the BCP and maintain themselves in the upper surface ocean, where light can drive photosynthesis. Meanwhile, many biotic and abiotic stresses act upon phytoplankton to force them downward. We have evidence that the propensity to combat the activity of the BCP is genetically encoded (Figure 1B). This project will seek to unravel the genetic mechanisms that phytoplankton employ to fight the BCP and understand how external stresses can overpower these mechanisms. You will combine cutting-edge high-throughput genetics with whole genome sequencing to identify genes required for buoyancy in model marine phytoplankton. You will then validate these genes by standard genetic manipulation and test the effect of a range of abiotic and biotic stressors on these mutants. Your data will have strong implications for our understanding of the Earth’s carbon cycle.


University of Warwick


  • Organisms and Ecosystems


Project investigator

  •  Dr. Richard Puxty



  •  Prof. David Scanlan

How to apply


You will use a combination of cutting-edge high-throughput genetics [3] and laboratory evolution experiments [4] to screen for novel buoyancy traits in model phytoplankton. You will then validate these mutants by standard genetic manipulation as established in the supervisor’s laboratories [5]. Characterisation of mutants will involve combinations of transcriptomic and proteomics. Together you will become expert in microbiology, microbial genetics, molecular cloning and next generation sequencing.

Training and skills

Training will be provided in the above techniques that have been developed in the Puxty and Scanlan labs. Many of these techniques will involve transferable technical skills including use of robotics and genetic manipulation.

Partners and collaboration

The supervisors are world-leading experts in marine molecular biology. We frequently publish in high profile interdisciplinary journals (e.g. Nature Plants, Current Biology, Proc. Natl. Acad. Sci. USA) and field specific high impact journals (e.g. The ISME Journal). You will belong to a larger group of environmental microbiologists in the department of life sciences’ environment theme. ( These groups occupy a large shared lab area and as such there is continuous collaborations and opportunities for career development within the theme. Current research in the groups is funded by NERC and generous start-up award to Dr. Puxty.

Dr Puxty’s group:

Prof Scanlan’s group

Further details

Applicants from the UK or the EU are eligible. Applicants should hold a BSc and/or MSc degree in relevant subjects. Informal enquires can be made to Dr Richard Puxty ( or Prof. David Scanlan (). Details of how to apply can be found at

Possible timeline

Year 1

Perform high-throughput genetic screen to identify gene candidates required for buoyancy in model marine phytoplankton

Year 2

Verify these gene candidates by classical reverse genetics.

Year 3

Test the affects abiotic and biotic stresses on capacity for buoyancy in wild type cells and mutants lacking buoyancy genes

Further reading

[1] Guidi, L et al., 2016. Plankton networks driving carbon export in the oligotrophic ocean. Nature, 532, 465-470.

[2] Boyd, P.W., Hervé, C., Levy, M., Siegel, D.A, Weber, T., 2019. Multi-faceted particle pumps drive carbon sequestration in the ocean. Nature, 568, 327-335.

[3] van Opijnen and Camilli, A., 2013. Transposon insertion sequencing: a new tool for systems-level analysis of microorganisms. Nature Reviews Microbiology 11, 435–442.

[4] Rainey, P and Travisano, M. 1998. Adaptive radiation in a heterogeneous environment. Nature, 394 69-72.

[5] Ostrowski et al. 2010. PtrA is required for coordinate regulation of gene expression during phosphate stress in a marine Synechococcus. ISME J., 4, 908-921.


Should COVID delay lab work, the student will mine already available high throughput genetic screens to identify genetic determinants of buoyancy.