Page 50 - Advances in bioenergy the sustainability challenge

approaches to metabolic engineering will be needed to increase yields and productivity
without adversely affecting cell function. Nonetheless, a biofuel that chemically resembles
petroleum fuels and can easily be integrated into existing technology has the potential to
quickly become a relevant component of the biofuel industry.

CONCLUSION

A systems-level interdisciplinary approach is necessary for effective strategies to tackle
today's global energy and environmental problems. The tools and strategies of metabolic
engineering are well suited for addressing the persistent challenges facing a successful
transition away from petroleum transportation fuels. As such, metabolic engineering will be
instrumental in developing the next generation of cost-effective and robust transportation fuels,
which will come from cheaper, more sustainable feedstocks and have better fuel
characteristics.

It remains to be seen what processes and technologies will successfully establish sustainable
alternatives to petroleum transportation fuels. However, because of obstacles in current
feedstocks and fuels, it is necessary to continue research in technologies that can overcome
existing limitations. Metabolic engineering is uniquely poised to develop and implement the

next-generation biofuels using a systems-level approach from multiple disciplines.
Furthermore, metabolic engineering allows us to explore unconventional strategies that are
naturally uncommon: nonfermentative production of branched higher alcohols, cellodextrin

transport for xylose and glucose cofermentation, and derivatization of fatty acid products.
Radical pathway manipulation is also on the horizon: engineering of nitrogen flux for the
conversion of protein into biofuels could further improve overall yields while recycling
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reduced nitrogen ; design of artificial nonphotosynthetic carbon fixation pathways could open
a new means of production processes without light (and thus land) as a limiting factor. 38
Metabolic engineering enables both promising and exciting opportunities for alternative
energy, which have the potential for great societal ramifications. It will also be central in the

long road ahead to develop these opportunities into robust, efficient industrial-scale
technologies.

REFERENCES

1. Stephanopoulos G. Challenges in engineering microbes for biofuels production. Science
2007, 315:801–804.

2. Bailey JE. Toward a science of metabolic engineering. Science 1991, 252:1668–1675.

3. Stephanopoulos G. Metabolic fluxes and metabolic engineering. Metab Eng 1999, 1:1–11.

4. Tyo KE, Alper HS, Stephanopoulos GN. Expanding the metabolic engineering toolbox:
more options to engineer cells. Trends Biotechnol 2007, 25:132–137.