Biomass Recalcitrance

What is Recalcitrance?

recalcitrance and BESC

Biomass recalcitrance is the central theme at BESC. Using innovation and understanding to overcome this barrier will lead to multiple societal benefits, including a broad range of biofuels and bioproducts.

Biomass recalcitrance is the resistance of plants to degradation or deconstruction, which enables access to a plant’s sugars. The starch from corn grains or simple sugars from sugarcane and beets are currently the primary sources of ethanol fuel production. These sugars are used directly for ethanol fermentation, largely because they are easy to access. Structural sugars contained in plant fibers (e.g., the remaining corn stalks or stover, grasses, and wood) also could be harnessed to produce ethanol, but they are tightly enmeshed in the cell wall structures of the plant material. Gaining access to these complexed sugars requires overcoming the plant’s resistance to degradation or recalcitrance. Understanding the scientific basis of this recalcitrance underpins the overall goal of the BioEnergy Science Center (BESC) to eliminate it as an economic barrier to cost-effective production of biofuels and bioproducts.

Importance of Biomass Research

Alternative fuels from renewable, widely abundant lignocellulosic biomass—plant stalks, trunks, stems, and leaves—are expected to significantly reduce U.S. dependence on imported oil while enhancing national energy security and decreasing the environmental impacts of energy use. Ethanol and advanced biofuels from lignocellulosic biomass are renewable alternatives that can increase domestic production of transportation fuels, revitalize rural economies, and reduce carbon dioxide and pollutant emissions relative to petroleum-based fuels.

Lignocellulosic biomass can be converted to fuels and other chemicals by a variety of routes, including (1) thermochemical processes involving reactive intermediates other than sugars (e.g., synthesis gas and pyrolysis oil), (2) fermentative processes that overcome recalcitrance primarily by nonbiological means (e.g., acid hydrolysis, phosphoric acid swelling, and ionic liquid pretreatments), and (3) fermentative processes that overcome recalcitrance with key biotechnology-driven advances. BESC research is focused on the third approach—particularly the development of less recalcitrant plants and microbes that more effectively convert lignocellulose—to overcome the recalcitrance barrier.

BESC Approach

Transformative advances in understanding recalcitrance require detailed knowledge of the chemical and physical properties of biomass that influence its resistance to degradation. Consequently, BESC research has been aimed at determining:

  • How these biomass properties can be altered by engineering plant biosynthetic pathways.
  • How biomass properties change during pretreatment.
  • How such changes affect biomass-biocatalyst interactions during deconstruction by enzymes and microorganisms.

Pioneering Research

BESC’s targeted focus on recalcitrance is singular among the Department of Energy’s three Bioenergy Research Centers. In this endeavor, BESC has made crucial progress toward understanding, manipulating, and managing plant cell wall recalcitrance and conversion. Notably, the BESC team proved the core concept that multiple genes control cell wall recalcitrance and that manipulating these genes potentially could yield perennial biofeedstocks that are easier to deconstruct. This research paves the way for improving feedstocks directly or by genetically assisted breeding. In conversion science, BESC researchers have identified and validated key genes for consolidated bioprocessing (CBP), a game-changing, one-step strategy that uses a single microbe or microbial consortium to both deconstruct biomass and ferment resulting sugars into fuels. Researchers are beginning to modify CBP target organisms to improve conversion and enhance products. In addition, they have shown the potential of thermophilic (heat-loving) microbes in biomass conversion and identified the critical deconstruction enzymes for key components of lignocellulosic biomass. Currently, the BESC team is demonstrating the action of improved CBP on modified plant cell walls.

As a result of the advances BESC has made to date, its cross-disciplinary and cross-institutional foundation, and its singular thematic focus, BESC is in a unique position to:

  • Bring to fruition the world’s most comprehensive efforts aimed at advancing understanding of the fundamentals of the multiple dimensions of recalcitrance.
  • Develop and field test less recalcitrant biomass feedstocks.
  • Realize the potential of microbial lignocellulose utilization.

This series of developments includes an unprecedented opportunity to examine the combined benefits of plants and microbes engineered to overcome recalcitrance, and to evaluate milder biomass pretreatments that are tuned to the properties of new feedstocks and biocatalysts.

BESC’s current progress and potential future contributions are facilitated by an integrated management structure that is organized into three research focus areas: (1) Biomass Formation and Modification, (2) Biomass Deconstruction and Conversion, and (3) Enabling Technologies—all supported by the best scientists in these outlined disciplines from across multiple institutions.


BioEnergy Science Center one of three DOE Bioenergy Research Centers established by the U.S. Department of Energy.