Switchgrass cultivated during a year of severe drought inhibited microbial fermentation.
Investment in plant-derived sustainable biofuel sources could contribute to a near-term solution toward U.S. energy security and independence. However, weather conditions have the potential to greatly affect yearly biomass production. When plants are grown under water-stressed conditions, reduction in photosynthesis and slower growth are exhibited, leading to decreased biomass production. In this study researchers examined the effect of weather on biofuel production by comparing switchgrass and corn stover harvested after a year of major drought and after 2 years of normal precipitation (2010 and 2013).
The study is the first linking variation in environmental conditions during bioenergy crop growth to potential detrimental effects on fermentation during biofuel production. This underscores the need for the development of biofuel production systems able to tolerate changes in precipitation and water availability as well as robust fermentation processes.
In response to the 2012 severe Midwestern drought, soluble sugar accumulated in switchgrass at significantly higher levels in comparison to non-drought period years. These sugars were chemically changed during the pretreatment stage, the step which opens up the physical structure of the plant cell wall. The soluble sugars chemically changed by reacting with the ammonia-based pretreatment chemicals to form highly toxic compounds known as imidazoles and pyrazines. The formation of toxic compounds during the pretreatment stage inhibited conversion, the final step where intermediates such as sugars are fermented into biofuel by microorganisms, such as the microbe S. cerevisiae. However, it may be possible to overcome this issue by 1) removing the soluble sugars prior to pretreatment or 2) using microbial strains resistant to the toxic effects of imidazoles and pyrazines. This study demonstrates that while there are benefits to growing bioenergy crops on marginal lands to avoid competition with food crops, the plants grown there may experience higher levels of stress resulting in deleterious impacts on microbes during biofuel production. To develop sustainable biofuel production systems, the deleterious effects of stress, such as fluctuations in precipitation and water availability, must be mitigated. This research helps to provide an understanding of the effects of drought stress on switchgrass and is relevant to DOE’s energy and environmental missions.
Kent Peters, Ph.D.
Program Manager Biological Systems Sciences Division
Office of Biological and Environmental Research
Office of Science
U.S. Department of Energy
Rebecca Garlock Ong
Assistant Professor, Chemical Engineering - Michigan Technological University
This work was funded by the DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science DE-FC02-07ER64494). Additional funding for L.G.O. is under DOE OBP Office of Energy Efficiency and Renewable Energy (DE-AC05-76RL01830).
R.G. Ong, A. Higbee, S. Bottoms, Q. Dickinson, D. Xie, S.A.Smith, J. Serate, E. Pohlmann, A.D. Jones, J.J. Coon, T.K. Sato, G.R. Sanford, D. Eilert, L.G. Oates, J.S. Piotrowski, D.M. Bates, D. Cavalier, and Y. Zhang, “Inhibition of microbial biofuel production in drought-stressed switchgrass hydrolysate.” Biotechnology for Biofuels 9, 237 (2016) [DOI: 10.1186/s13068-016-0657-01] (Reference link)
Great Lakes Bioenergy Research Center
SC-23.2 Biological Systems Science Division, BER
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