Page 40 - Advances in bioenergy the sustainability challenge

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Metabolic Engineering: Enabling Technology for

Biofuels Production

Mitchell TaiGregory N. Stephanopoulos
Department of Chemical Engineering, Massachusetts Institute of Technology, USA

ENGINEERING THE FUTURE OF BIOFUELS

The past few years have introduced a flurry of interest over renewable energy sources.
Biofuels have attracted attention as renewable alternatives to liquid transportation fuels. There
are numerous potential advantages over fossil fuels: sustainable supply, diversification of
energy sources, energy independence and security, rural development, and reduction in
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greenhouse emissions. However, achieving adequate scale requires a tremendous effort in
research and development beyond what has thus far been achieved. The field of metabolic
engineering is well suited to develop the future technologies that will give us widespread,
cost-effective, and sustainable transportation fuels.

Metabolic engineering is the improvement of cellular activities by manipulation of metabolic
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networks through the use of recombinant deoxyribonucleic acid technology. Interdisciplinary
advances in metabolic engineering have yielded powerful strategies and methods to understand
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and manipulate whole metabolic pathways with confidence. To date, numerous efforts have
successfully engineered and optimized metabolic networks to produce high-value targets for
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use in the pharmaceutical and fine chemicals industries. However, attention is now being
turned toward commodity-scale processes, which require both cost-efficiency and robustness. 1

Currently, the most prevalent biofuels are ethanol produced from corn or sugarcane and
biodiesel produced from vegetable oils. Under current production processes, however, neither
biofuel is economically competitive or well integrable into existing petroleum-based
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technologies and infrastructure. Two developmental challenges underpin these shortcomings:
(1) the need for a better feedstock and (2) the need for a better fuel. However, these challenges
also represent key opportunities to develop the next generation of biofuel technologies. A
central element in these technologies will be the use of metabolic engineering to develop the
biological platforms that produce these biofuels.

Engineering for Improved Feedstocks

For the past few years, production of ethanol from corn and biodiesel from vegetable oils has

been increasing rapidly. Last year, the United States production capacity of corn ethanol
exceeded 13 billion gallons per year (bgy), approaching 10% of the national gasoline
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demand. Meanwhile, global biodiesel production is approaching 5.0 bgy, with a majority