How climate impacts the role of viruses

Degree type

PhD

Closing date

10 October 2022

Campus

Hobart

Citizenship requirement

Domestic/International

About the research project

Background

Sea ice itself contains diverse and productive microbial communities that can account for up to 30% of the annual primary productivity of the Southern Ocean. As the ice melts, it releases a vast algal biomass into the surface waters of the ocean which then initiates an annual 'ice edge bloom'. For much of the year deep mixing and low light levels makes much of the Southern Ocean unproductive. However, for a brief period in spring, the melting ice causes an increase in light and nutrients and a sharp reduction in the depth of mixing; these factors provide transient conditions that favour the rapid development of highly productive ice edge blooms.

Sea ice not only contains a large microalgal biomass, it also contains abundant bacteria and viruses. However, while the physiology and ecology of the algal component is well understood, less is known of the bacterial and virus communities and their interactions with the sea ice algae.

Bacteria are responsible for nutrient recycling and secondary production. There is a tight coupling between microalgae, bacteria, viruses and protozoa. In open systems as much as 80% of the carbon fixed during photosynthesis remains in the loop. The microbial loop runs on DOM. Microalgae produce DOM which is taken up by the bacteria. The protozoans graze on the bacteria, releasing nutrients

Viruses are responsible for 10-30% of daily bacterial mortality but in some circumstances this can reach up to 100. Viral lysis of bacteria and microalgae increases the pool of dissolved organic matter and thus turbo charges the microbial loop. These changes in the organic matter flow induced by viral lysis have been termed the 'viral shunt'. Although most attention has been given to the infection of prokaryote hosts, phytoplankton infection by viruses is estimated to reduce primary production by up to 78%. Viruses are now known to be widespread in microalgae and found to infect all major phytoplankton groups, including diatoms and dinoflagellates Most identified phytoplankton viruses have been classified as dsDNA viruses, although ssDNA and ssRNA viruses have been found to be widespread in diatom and dinoflagellate taxa.

Virus infection rates in marine ecosystems is thought to be largely host density-mediated, i.e the more abundant a species becomes the more likely it is that it will interact with a virus, become infected and then suffer cell lysis. Thus, viruses are seen to have the ability to control species succession and maintain maximum biodiversity; this became known as the 'kill the winner' scenario. However, rather than always causing cell lysis, some viruses transfer their DNA into the host's genome without killing it, a process known as lysogeny. This mechanism enables the virus to coexist with a rare host over many generations and is thought to be increasingly important in oligotrophic environments.

When the sea ice begins to melt in spring, the sea ice algae are released into the surface sea water where they contribute to dense blooms. However large numbers of bacteria and viruses are also released and these have the potential to directly impact the emerging phytoplankton blooms. Climate change (including temperature, pH, macro and micronutrients and light) is forcing many changes on these communities, some of which are likely to enhance susceptibility to virus infection.

The major hypotheses to be tested in this project are:

  1. Bacterial and virus interactions with sea ice algae control biodiversity, succession and biomass
  2. Bacteria and viruses determine species succession and biomass of the phytoplankton during marginal ice zone blooms
  3. Ocean warming and acidification will enhance virus infection rates in ice edge phytoplankton and sea ice algae

These hypotheses will initially be tested during the ACEAS Marginal ice zone voyage and the Chinese Xuelong2 summer voyage (2023). During these voyages contemporary interactions will be examined and characterised. The flux of viruses, bacteria and phytoplankton cells from the sea ice to the water column will be measured. Regular sampling for virus, bacteria and phytoplankton will be made. Measurements will be made by flow cytometer in the laboratory. Meta-transcriptomics and TEM will be used to examine phytoplankton infection rates. Both DNA and RNA viruses will be examined. An on-board time series will allow the examination of how the bloom develops and measure changing viral infection rates. Laboratory experiments at IMAS will be used to determine whether increasing temperature and pH causes an increasing susceptibility to viral infection. Laboratory experiments, using a low iron ice tank, will be used to determine whether viral infection increases if sea ice algae are iron-stressed.

Primary Supervisor

Meet Professor Andrew McMinn

Funding

Applicants will be considered for a Research Training Program (RTP) scholarship or Tasmania Graduate Research Scholarship (TGRS) which, if successful, provides:

  • a living allowance stipend of $28,854 per annum (2022 rate, indexed annually) for 3.5 years
  • a relocation allowance of up to $2,000
  • a tuition fees offset covering the cost of tuition fees for up to four years (domestic applicants only)

If successful, international applicants will receive a University of Tasmania Fees Offset for up to four years.

As part of the application process you may indicate if you do not wish to be considered for scholarship funding.

Eligibility

Applicants should review the Higher Degree by Research minimum entry requirements.

Additional eligibility criteria specific to this project/scholarship:

  • Applicants must be able to undertake the project on-campus

Selection Criteria

The project is competitively assessed and awarded.  Selection is based on academic merit and suitability to the project as determined by the College.

Additional essential selection criteria specific to this project:

  • Microbiology laboratory experience
  • Critical thinking skills; relevant science degree with microbiology; good communication (writing, oral) and quantitative skills

Additional desirable selection criteria specific to this project:

  • Experience with omics research
  • Experience working with viruses

Application process

There is a three-step application process:

  1. Select your project, and check you meet the eligibility and selection criteria;
  2. Contact the Primary Supervisor, Professor Andrew McMinn to discuss your suitability and the project's requirements; and
  3. Submit an application by the closing date listed above.
    • Copy and paste the title of the project from this advertisement into your application. If you don’t correctly do this your application may be rejected.
    • As part of your application, you will be required to submit a covering letter, a CV including 2 x referees and your project research proposal.

Following the application closing date applications will be assessed within the College. Applicants should expect to receive notification of the outcome by email by the advertised outcome date.

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