Monday, August 2, 2010
Pacific Concourse (Hyatt Regency San Francisco)
To effectively convert lignocellulosic biomass to fermentable sugars by simultaneous saccharification and fermentation for ethanol production, it will be necessary to utilize a yeast species, such as Candida molischiana, that can convert glucose and xylose to ethanol. Unfortunately, this yeast species is not thermotolerant in that it grows slowly at temperatures above 35oC. For this species to be suitable for simultaneous saccharification and fermentation, a more thermotolerant C. molischiana strain will have to be isolated. In this investigation, a procedure was developed for the isolation of a C. molischiana mutant strain capable of growth at 45oC. The strain utilized in this study was C. molischiana ATCC 2516. The strain was grown on YEPD (1% yeast extract, 2% peptone and 2% glucose) or a yeast nitrogen base minimal medium. The strain was subjected to nitrous acid mutagenesis for 60 minutes at 35oC with outgrowth occurring in YEPD medium for 48 hours at 35oC. After the cells were washed, they were spread onto 0.17% yeast nitrogen base minimal medium agar plates containing 0.5% ammonium sulfate, 0.1% 2-deoxyglucose and 2% raffinose. Following incubation of the plates at 35oC for 5-8 days, colonies on the plates were tested for their thermotolerance. One colony grew on solid YEPD medium at 45oC. In liquid YEPD cultures, the mutant strain grew faster at 45oC than its parent strain. In summary, the isolation of a thermotolerant mutant strain of C. molischiana ATCC 2516 was possible using a protocol involving chemical mutagenesis and resistance to glucose analogue.