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Issue 3
8th
February 2010
C&I Magazine
Synthetic biology breakthrough may fuel future
Andrew Turley,
08/02/2010
Bacteria that can produce ‘high-energy’
biofuels, such as biodiesel, direct from
simple sugars, or light up in coordinated
waves could provide a turning point in
the fortunes of synthetic biology – a
field that has so far failed to fulfil its
early promise.
Researchers from the University
of California, US, engineered E coli
to produce biodiesel, or fatty esters,
from glucose, without the need for
other carbon sources (Nature 2010,
463, 559). They then engineered the
same strain to express hemicellulases,
enzymes that break down
hemicellulose, a step towards bacteria
that can produce biodiesel direct from
cellulosic biomass.
Global biodiesel consumption is
more than 2bn gallons/year. Companies
make fatty esters commercially by
reacting triglycerides from vegetable
– or less commonly animal – oils with
alcohols.
But using vegetable oils as a
fuel feedstock is economically and
environmentally problematic, critics
say. For example, as farmers switch
to crops for biodiesel, food production
could fall, exacerbating food scarcity
and driving up prices. In addition, high
demand for energy and land scarcity
could encourage farmers in ecologically
rich, but economically poor, regions
to cut down forests to make way for
crops.
Biodiesel can be made from
cellulosic biomass, waste plant
material, such as wood chips, or nonfood
crops, such as grasses. But, using
current methods, it is more difficult and
more expensive.
Scientists hope to bring the cost
down by getting bacteria to do the
hard work. E coli, for example, will
grow on plant sugars. In earlier work,
scientists made E coli that produced
ethanol, which they used to chemically
convert fatty acids into fatty esters
(Microbiology 2006, 152, 2529). But
fatty acids are not a commercially viable
feedstock, which limits the potential of
this approach.
Therefore, the Californian
researchers redirected the E coli fatty
acid metabolism towards fatty esters
and other commercially useful fuel
and chemical products. Crucially, they
encouraged the bacteria to produce
more fatty acids, while expressing key
enzymes that caused esterification.
Commercially viable bacteria
that performed all the steps in the
chain inside their cells – bacteria for
‘consolidated bioprocessing’ – would
make biofuel production easier and
cheaper, the researchers say in the
paper. ‘This engineering strategy
supports yields of these products within
an order of magnitude of that required
for commercial production,’ they add.
Synthetic biology
They carried out the work with a grant
from LS9, a US biotech company
focusing on ultraclean fuels and
sustainable chemicals.
‘Significant hurdles remain to
demonstrate yield, productivity and
cost performance consistent with fuel
economics,’ says Johan van Walsem,
vp for strategy and commercial
development at US biotechnology
company Metabolix. ‘Both capital and
operating costs are likely to be much
higher than that of relatively simple
ethanol fermentation and remains a
hurdle to commercialisation. The same
technology can also provide valueadded
chemicals, such as detergent
alcohols, providing a different
commercial entry point.’
Synthetic biology is a busy, diverse
field, in which scientists combine
science and engineering to make
biological machines that perform
functions using the minimum of parts.
Advances have been made towards
the production of clean, sustainable
biofuels, cheap drugs and synthetic
organs, but the challenges have proved
greater than many initially envisaged.
In other research, scientists at
the same institution have engineered
E coli that produce fluorescent
molecules in synchrony to generate
coordinated waves of light (Nature
2010, 463, 326). They exploited a
bacterial communication system
known as quorum sensing to create
a complex network of genes, proteins
and signalling molecules that act as a
‘molecular clock’. In natural systems,
quorum sensing is used to trigger group
behaviour, such as plaque formation,
when a critical population is reached,
which makes cooperation worthwhile.
In previous work, scientists made E
coli with visible internal time-keeping,
but a universal time was needed for
the group activity – and that meant
effective communication.
The work could improve our
understanding of sleeping and
learning, as well as the symptoms of
certain disorders, such as Parkinson’s,
Huntington’s and Alzheimer’s disease.
It could also lead to cell implants that
can deliver drugs at specific times, in
precise doses, says Martin Fussenegger,
a biotechnology professor at ETH Zurich
in Switzerland, in a Nature N&V article
(Nature 2010, 463, 301). ‘The use of
the rhythmic synthesis of molecules…
as a pacemaker to coordinate the
behaviour of individual oscillators
in a growing population of cells is
a quantum leap in molecular-clock
design,’ he adds.