Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/22/2009
Publication Date: 7/22/2009
Citation: Christopher, L.P., Gibbons, W., Bleakeley, B., West, T., Hughes, S.R., Sani, R.K., Bang, S.S. 2009. Development of thermotolerant consolidated bioprocessing microbes for cost-efficient cellulosic ethanol production [abstract]. Industrial Biotechnology and Bioprocessing. Talk #4. p. 1. Interpretive Summary:
Technical Abstract: The Center for Bioprocessing Research and Development (CBRD) in South Dakota has been established with the objective to conduct biomass research for lignocellulose bioprocessing to biofuels and biochemicals. Over sixty faculty, staff and their students from eight departments at the South Dakota School of Mines and Technology and South Dakota State University representing the fields of agriculture and biosystems engineering, biochemistry, chemical and biochemical engineering, industrial microbiology, mechanical engineering, and plant science work to achieve the next generation of advances required to fully realize the creation of the lignocellulose based bioindustry. The mission of the Center as the leading institution in South Dakota in the development and technology transfer of new bioenergy technologies is to reduce the national dependence on imported fuels of environmental concern and stimulate economic growth in the region. For development of more efficient and economically viable biomass bioconversion technologies, scientists and engineers at CBRD are utilizing extremophilic microorganisms with distinctive cellulolytic capabilities isolated from the former Homestake Gold Mine (now known as the NSF Deep Underground Science and Engineering Laboratory, DUSEL), located in proximity to Rapid City. The deep subsurface of the mine (8000 ft) offers extreme environments for microorganisms introduced by mining activities over more than 125 years. CBRD researchers have recently grown wood-rotting microbes from the 4850 ft level which secreted lignocellulose deconstructing enzymes with high temperature optima (70-80 deg C) and stability (25% residual activity after incubation at 60 deg C for 2 weeks). Cellulose-degrading mesophilic and thermophilic pure cultures belonging to the genera Brevibacillus, Paenibacillus, Bacillus, and Geobacillus were isolated from enrichment cultures, and selected cultures were studied for enzyme activities. The extremophile isolates could provide a powerful source of novel enzyme cocktails for improved lignocellulose degradation and cost-effective production of renewable bioenergy in South Dakota. To overcome limitations related to the low bulk density of biomass, CBRD researchers are developing a novel bioreactor for high solids fermentation that will provide the advantages of increased product concentration, lower energy requirements, increased productivity, and smaller effluent volumes. The use of thermotolerant yeasts in conjunction with cellulolytic and hemicellulolytic extremozymes will enable both the saccharification and fermentation to proceed simultaneously at temperatures closer to optimal. Added benefits will be reduced cooling costs and decreased risk of contamination. To further enhance the ethanol tolerance, yeasts are exposed to chemical mutagens to enrich for mutants with altered membrane permeability. Mutants resistant to nystatin or 2-deoxyglucose may have increased tolerance to ethanol. Selected mutants are then screened for enhanced ethanol tolerance in media containing progressively higher ethanol levels. A novel yeast engineering strategy has been employed which involves metabolically engineering of thermotolerant yeasts to express lignocellulose deconstructing genes and providing the capability to utilize both five and six carbon sugars.