Battling Cellulose

Insights into biomass could improve biofuel production.

Growing societal responsiveness to the long-term environmental impact of human activities has increased the drive to develop sustainable and ­carbon-­neutral approaches to energy production. One of the most attractive possible substitutes for petroleum-derived products, such as oil and commodity chemicals, is plant biomass.

Credit: Technology Review

Feedstocks such as corn and sugarcane have been bred over thousands of years for their capacity to store high levels of starch (in the case of corn kernels) or sucrose (in the case of sugarcane stalks). Current industrial processes for biofuel production depend on traditional methods of converting these ­simple but valuable sugar, starch, and oil feedstocks into liquid fuels, but these techniques often leave behind a large amount of more chemically complex agricultural material as waste.

The energy in biomass is derived by means of photosynthesis, in which plants use energy from the sun to synthesize carbohydrates from carbon dioxide and water. Thus, realizing the full potential of biofuels depends directly on utilizing more of the carbon or carbon dioxide equivalents found in biomass. Most of the carbon in a plant is stored as lignocellulosic biomass, which is typically considered crop residue. Made up of cellulose, hemicellulose, and lignin polymers, these parts of the plant evolved to protect and preserve the integrity of plant structures, so they are difficult to break down.

Existing strategies for processing and transforming this waste are limited, but many different ways of converting biomass to energy are under investigation. Much attention has focused on biological methods of breaking down lignocellulose into its constituent parts. Microbes and microbial communities have evolved to exploit biomass as a nutrient source, and they have developed enzymatic systems that degrade lignocellulose and metabolize the resulting molecules. But efforts to engineer microbes that can efficiently degrade lignocellulose will require more fundamental research on the way these complex systems function at a molecular level.

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In parallel with this work, advances in functional plant genomics and engineering should lead to more rapid development of new crops with desirable energy-related traits, such as structurally modified cell walls that can be more easily degraded by emerging methods of lignocellulose processing.

Our laboratory is focused on elucidating the underlying design principles that explain complex chemical functions such as the multienzyme degradation of lignin. By combining fundamental biochemical studies with the tools of metabolic engineering and synthetic biology, we hope to learn how to rationally design new chemical functions in living systems.