SUSTAINABILITY AND THE ENVIRONMENT: BIOTECHNOLOGY
WASTE FIND BRINGS
PET TO HEEL
Plastic pollution is now widely recognised as
one of the worst environmental calamities
of our time. Over the past 70 years more
than 8.3 billion metric tonnes of plastic
has been produced globally, and almost all of it remains
in the environment – particularly in the ocean because
of the ‘scouring’ effect of river catchments that collect
discarded rubbish in towns and cities and disgorge it,
eventually, into the sea.
For marine scientists, plastic pollution has surpassed
crisis level and is now an existential threat to ocean life –
at a time when the ocean is going to be more vital than
ever for human food security as terrestrial agriculture
strains under the pressure of climate change.
This grim scenario brings into sharp relief the
importance of groundbreaking research by the
University of Portsmouth in engineering a naturally
occurring enzyme that can break down one of the most
abundant plastics, polyethylene terephthalate or PET,
used in single-use drink bottles, clothing and carpets.
It has been estimated that it will take 450 years for a
PET drink bottle to break down naturally in the ocean,
and the EU alone consumes 46 billion PET drink bottles
Not surprisingly, the University’s enzyme research
– now housed within the newly established Centre for
Enzyme Innovation (CEI) – has attracted worldwide
attention and acclaim among scientists, governments
and also the plastics industry itself. The team was
recently awarded the Times Higher Education STEM
Research Project of the Year.
Like many scientific breakthroughs, the discovery
was partly serendipitous. Researchers at the
University led by Professor John McGeehan – and
in partnership with the US Department of Energy’s
National Renewable Energy Laboratory (NREL) – were
investigating the inner workings of PETase, an enzyme
discovered in a Japanese bottle-recycling facility in
2016. This PETase enzyme appeared to be breaking
down plastic and the team was trying to understand
how it had evolved to digest artificial plastics, given
PET has only been around since the 1940s – a very
short period for an evolutionary adjustment.
The researchers could see that the structure of
the enzyme was similar to one evolved by bacteria to
break down cutin, a natural polymer used by plants
as a protective coating. The team was manipulating
the enzyme to explore this connection when they
unintentionally improved its PET-digesting ability.
Collaborating NREL scientists Dr Bryon Donohoe
and Dr Nic Rorrer subsequently tested PETase on PET
samples from drink bottles. Observing with an electron
microscope, they saw the PETase enzyme begin
degrading the pieces of PET plastic after just four days.
The researchers knew they were only at an early
stage and that further engineering could potentially
make the enzyme work much faster and be a genuine
tool for revolutionising plastics recycling.
Professor McGeehan and his team are now working
on improving this enzyme for industrial-scale use, while
continuing the search for new enzymes that can break
down other highly-polluting plastics.
The research is being facilitated by the Portsmouth
researchers’ access to the UK’s national synchrotron
in Oxfordshire, called the Diamond Light Source. The
synchrotron’s I23 beamline uses intense beams of
X-rays 10 billion times brighter than the sun to act
as a microscope powerful enough to make individual
atoms visible. It reveals the 3D structures of nature’s
molecules of life, allowing researchers to apply the
tools of protein engineering and directed evolution to
continue to improve the PETase enzyme.
It is of the
that the UK
the need to
to take our
– John McGeehan
ISSUE 1 / 2020