Recalcitrance is the resistance of plant biomass to degradation, which allows access to the sugars in lignocellulosic biomass.
Historically, the term "recalcitrance" was coined to describe an overall phenotypic trait of biomass, namely the degree of difficulty in obtaining access to sugars complexed in the plant cell wall. However, based on new knowledge about cell wall chemistry, structure, and biochemistry, BESC researchers have redefined recalcitrance as a phenomenon in terms of pathways and interactions, both in cell wall formation and bioconversion. This increasing knowledge of the scientific basis of recalcitrance underpins the overall BESC goal of eliminating it as an economic barrier to cost-effective biofuel production.
Alternative fuels from renewable cellulosic 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 cellulosic 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.
According to U.S. Secretary of Energy Ernest Moniz, “By partnering with industry and universities, we can help make clean, renewable biofuels cost competitive with gasoline, give drivers more options at the pump, and cut harmful carbon pollution.” The primary source of U.S. ethanol fuel production today comes from corn grain, but the biofuels of the future will come from other biomass sources including specially designed bioenergy feedstocks. Woodchips, grasses, cornstalks, and other cellulosic biomass are widely abundant but more difficult to break down into sugars than corn grain because of the lignin present in these forms of biomass.
Although cellulosic ethanol production has been demonstrated at the pilot scale, developing a cost-effective, widespread, and commercial-scale cellulosic biofuel industry will require significant improvements in current production processes. Innovation stemming from advanced biotechnology-based research is key to accelerating needed improvements in the production of cellulosic biomass, its deconstruction into sugars, and conversion to biofuels.
Transformative advances in understanding recalcitrance require detailed knowledge of the chemical and physical properties of biomass that influence its resistance to degradation. BESC research has been aimed at determining:
Biomass recalcitrance is the central theme at BESC. Using innovation and understanding to overcome this barrier will lead to multiple benefits.
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.
BESC is organized into three research focus areas: (1) Biomass Formation and Modification, (2) Biomass Deconstruction and Conversion, and (3) Enabling Technologies—all supported by integrating activities.