Project proposal form – 2017 entry
Project title: Mind the Gap: microbe-microplastic interactions
Host institution: The University of Warwick
Theme: Anthropogenic Impact
Key words:
Supervisory team (including institution & email address):
Dr. Marco Polin, Physics Dept. University of Warwick, [email protected]
Dr. Joseph Christie Oleza, School of Life Sciences, University of Warwick, [email protected]
Project Highlights:
•
understand how marine microorganisms interact
with micron-size plastic debris
•
provide insights into the unexplained microplastic
gap in the oceans
•
develop interdisciplinary skills at the interface of
biology and physics
Overview (including 1 high quality image or figure):
We live in a plastic age where the consumption of
synthetic polymers is relentlessly increasing every
year. Most of the consumed plastic is of single use
and, hence, will rapidly end up as waste. Mismanaged
plastic waste inevitably enters aquatic systems and
ultimately is washed into the oceans: recent estimates
show that ~10 million metric tons were dumped in the
seas just in 2010, with a predicted 10-fold increase by
2025 [1]. Most plastics are highly durable and
therefore expected to persist in the environment for
centuries.
The ultimate fate of marine plastics and its
environmental impact is not well understood. Recent
global surveys estimate that the plastic currently
floating in the oceans accounts for only ~1% of the
total expected marine plastic debris that has been
dumped by humans during the past 50 years [2]. The
fate of the remaining 99% is unknown.
Marine plastics fracture and break due to weathering,
and therefore small debris should be much more
abundant than large ones. This has indeed been
observed, but only down to a size of ~2mm. Below
that size a “microplastic gap” appears: a sharp cutoff
at the millimetre scale with sub-millimetre size debris
strikingly under-represented [2,3].
What processes are responsible for the development
of the microplastic gap? Could these be the key to
understand the fate of the missing plastic?
One interesting hypothesis is that the gap is a
consequence of two possible biological processes: i)
fast sinking due to changes in buoyancy following
colonisation by microorganisms; and ii) direct uptake
of microplastics by plankton. These two processes are
most likely complementary, rather than mutually
exclusive. The latter in particular has been partly
supported by direct laboratory observations of
copepods feeding on 20um-size plastic particulate [4].
At the same time, we have recently shown that motile
microorganisms can easily come into close contact
Figure 1: Interactions between plastic debris and
microorganisms. a) A 1µm polystyrene particle being
entrained by a microalga; b) bacterial colonies (blue) on the
surface of a piece of polyethylene (red).
with micron-size passively drifting particulate while
swimming. This would provide an easy route to
microplastics uptake for the multitude of phagotrops
in the oceans, providing a further direct route for
plastic to enter the global food web.
Year 3: Establishment of protocols for ingestion
experiments. Systematic characterisation of the
dynamics of ingestion and retention; investigation of
possible modification to physico-chemical properties
of ingested plastic.
Methodology:
Further reading:
This Ph.D. project will develop critically our
understanding of the relation between sub-mm
plastic particulate and marine microorganisms, with
the aim of clarifying the mechanisms leading to the
emergence of the microplastic gap. Your research will
adopt a two-pronged approach, studying both the
large and the small ends of the size spectrum. For
large plastic objects (~1000-100um), the student will
study quantitatively the dynamics of microorganismal
colonisation depending on size and plastic type. Size
has already been shown to have a strong effect e.g.
on microbial colonisation and processing of oil
microdroplets from platform spillages [5]. At the small
end (<10um), the student will focus on the uptake of
plastic microparticles by marine phagotrophs, already
reported anecdotally [6]. The student will start from
microfluidic and microscopy techniques already
available in the Polin lab [7] and will further
improve/refine them.
[1] J. R. Jambeck, et al., Science, 347, 768(2015).
[2] A. Cozar, et al., Proceedings of the National
Academy of Sciences (USA), 111, 10239(2014).
[3] www.sciencemag.org/news/2014/06/ninety-ninepercent-oceans-plastic-missing
[4] M. Cole, et al., Environmental Science and
Technology, 49, 1130(2015).
[5] Ongoing work by Stocker lab. See
http://stockerlab.ethz.ch/research/
[6] D. J. S. Montagnes, et al., Aquatic Microbial
Ecology, 53, 83(2008).
[7] R. Jeanneret, D. Pushkin, V. Kantsler, and M. Polin,
Nature Communications, 7, 12518(2016).
Training and skills: Maximum 100 words
Co-supervised by Dr. Marco Polin (Warwick, Physics
Department) and Dr. Joseph Christie-Oleza (Warwick,
School of Life Sciences), the project will require a
combination of experimental (general microbiology
wetlab) and theoretical/numerical skills (in particular
quantitative data analysis and programming). The
successful candidate will either already possess them
or be willing to learn enthusiastically.
Partners and collaboration (including CASE): The
project has the potential to become CASE, by building
links with industries involved in either plastic
production or waste management.
Possible timeline:
Year 1: Familiarisation with existing experimental
protocols, and establishment of new ones for:
formation and weathering of microplastics;
microbiology wetlab; microfluidics; microscopy.
Establishment of protocols for experiments on plastic
colonisation (large size) and ingestion (small size).
Year 2: Systematic experiments on colonisation of
plastic debris as a function of size and surface features
(e.g. roughness). Quantification of colonisation
dynamics,
species
abundance
and
spatial
heterogeneity of the biofilm.
Further details:
Enthusiastic applicants with 1st class BSc or MSci
degrees in Biology, Physics, or related fields. Previous
laboratory experience will be an advantage but is not
required. Programming skills are necessary at least at
a basic level. Contacts:
Marco Polin: [email protected]
Joseph Christie-Oleza: [email protected]