Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2004
Publication Date: 1/15/2005
Citation: Liu, Z., Slininger, P.J., Gorsich, S.W. 2005. Enhanced biotransformation of furfural and 5-hydroxymethylfurfural by newly developed ethanologenic yeast strains. Applied Biochemistry and Biotechnology. 121-124: 451-460. Interpretive Summary: Renewable biomass including agricultural residues is an attractive potential, low-cost feedstock for bioethanol production. However, one of the major barriers for using biomass conversion into ethanol is the yeast susceptibility to inhibitory compounds presented in the biomass acid hydrolysates. Additional detoxification steps using physical, chemical, or biochemical methods add cost and complexity to the process and generate additional waste products. Currently, no tolerant yeast is available against major inhibitors for bioethanol fermentation. To promote efficient bioethanol production, we are studying stress tolerance mechanisms to improve performance of yeast against fermentation inhibitors. During this course of study, we developed a method to adapt yeasts to major inhibitors. Using this method, we generated several new strains tolerant to the inhibitors at relatively higher levels. These newly adapted and more tolerant strains converted the inhibitors into less toxic compounds and produced normal yield of ethanol under controlled conditions. Therefore, no additional detoxification is needed using these tolerant strains. The method reported in this study impact a broad range of microbial research communities because it provides a strategic method for developing adapted strains against varied environmental stimulants in a short period of time. The developed strains and findings in this study impact bioethanol research and production communities because they provide materials and knowledge for further improvement of inhibitor tolerant yeasts for more cost-efficient biomass conversion to ethanol.
Technical Abstract: Furfural and 5-hydroxymethylfurfural (HMF) are representative inhibitors among many inhibitive compounds derived from biomass degradation and saccharification for bioethanol fermentation. Most yeasts, including industrial strains, are susceptible to these inhibitory compounds especially when multiple inhibitors are present. Additional detoxification steps add cost and complexity to the process and generate additional waste products. To promote efficient bioethanol production, we study mechanisms of stress tolerance, particularly to fermentation inhibitors such as furfural and HMF. We recently reported a metabolite of 2,5-bis- hydroxymethylfuran as a conversion product of HMF and characterized a dose-dependent response of ethanologenic yeasts to inhibitors. In this study, we present newly adapted strains that demonstrated higher levels of tolerance to furfural and HMF. Saccharomyces cerevisiae 307-12H60, 307-12H120, and Pichia stipitis 307-10H60 showed enhanced biotransformation ability to reduce HMF to 2,5-bis-hydroxymethylfuran at 30 and 60 mM; and S. cerevisiae 307-12-F40 converted furfural into furfuryl alcohol at significantly higher rates compared to the parental strains. Strains of S. cerevisiae converted 100% of HMF at 60 mM and S. cerevisiae 307-12-F40 converted 100% of furfural into furfuryl alcohol at 30 mM. Results of this study suggest a possible in situ detoxification of the inhibitors by using more inhibitor-tolerant yeast strains for bioethanol fermentation. Development of such tolerant strains provided a basis and useful materials for further studies on the mechanisms of the stress tolerance.