Termite guts to boost biofuels

Materials World magazine
,
1 Aug 2011
Man looking at termites on wood. Image courtesy of Purdue Agricultural Communication, USA/Tom Campbell

Termites may provide the key to breaking
down woody biomass for more efficient
biofuel production.

A team from Purdue University in West
Lafayette, USA, is using enzymes from the gut
environment of termites to improve processes
for the saccharification of second-generation
feedstocks.

Lead researcher Michael Scharf explains that
current biofuel production processes require a
lot of energy, which adds significant costs to
second generation ethanol production.

‘The market needs lignin-degrading technology
that operates at ambient temperatures
and does not generate hazardous waste.
Technology that can meet these needs has
the potential to reduce processing costs and
make ethanol more viable in the market.’

According to Scharf, current biorefinery pretreatment
operations use heat and/or
alkalinity to break lignin, solubilise
hemicellulose and isolate cellulose. The team
uses a cocktail of termite-derived enzymes to
combine the three steps into a single pretreatment
and saccharification process, and
reduce the need for heat, energy and alkalinity.

The group has created synthetic ‘recombitant’
enzymes produced out of genes sampled
from host termite tissues. To achieve this,
the termites graze on pine sawdust in 10-24
hour incubations. These enzymes include
two cellulases that act on cellulose and
hemicellulose, and a laccase that acts on lignin.

‘The laccase acts on lignin and the two
cellulases display a high level of collaboration
in simple sugar release (~300-fold synergy),’
alleges Scharf.

Termites were chosen because their digestive
tissues boast a complex cocktail of apparent
cellulase and lignin degrading enzymes. Termite
symbionts are also said to produce a rich complement
of cellulases and related enzymes.

The scientists have collaborated with protein
production company Chesapeake Pearl, based
in Maryland, USA, to create the synthetic
enzymes. The termite genes responsible for
creating the enzymes are inserted into a virus
and are then fed to caterpillars, which act
as ‘biological machinery’ to produce large
amounts of the recombinant enzymes. Another
insect was chosen because the recombinant
enzymes are said to have a high probability of
being correctly folded and processed.

While the researchers have been encouraged
by results at ‘test-tube level’, Scharf
notes, ‘We have not yet developed any commercial
technology, so we cannot comment
on efficiencies at the bioreactor level. Our
goals up to this point have been to understand
how termites and their symbionts accomplish
lignocellulose digestion, and to identify leads
for further development.’

Choosing the most important genes and
enzymes to pursue from the hundreds
available remains a challenge, says Scharf.
As such, the team intends to conduct
controlled, hypothesis-driven research to
determine which enzymes are the most viable
candidates.

Dr. Simon Cragg, of the School of Biological
Sciences in the University of Portsmouth, UK,
says, ‘If successful, this approach would
release simple sugars for which we already
have centuries of development in the technology
for generation of alcohols. Thus, a rather
unpromising material such as straw can be
converted to a liquid fuel. While we already
have a wide range of renewable energy
technologies for supplying fixed installations,
we have fewer options for transport. This
technology could help fill this gap.’

While complimentary of the study, Cragg
notes, ‘There is much to be done to bring the
insights generated to the point where pricecompetitive
fuel is generated. Particularly
challenging problems for developing these
ideas lie in the question of economically viable
feedstock processing and transportation.
Before enzymatic degradation, feedstocks will
almost certainly require reduction to easilydigested
particles, which demands significant
energy input. Parallel engineering efforts are
therefore needed to make a step change in
the efficiency of processing.’