Monday, July 27, 2009
P52
Adaptation of Pichia stipitis CBS 6054 to dilute acid pretreated aspen hydrolysate for improved ethanol yields
Stephanie L. Groves, Jill R. Jensen, Juan E. Morinelly, and Susan T. Bagley. Biological Sciences, Michigan Technological University, 1400 Townsend Dr,, Houghton, MI 49931
Pichia stipitis CBS 6054 is a natural xylose-fermenting yeast that can be used for the conversion of lignocellulosic sugars to ethanol. Adaptation was used to modify P. stipitis CBS 6054 for increased ethanol yields when grown on high percentages of dilute acid pretreated aspen hydrolysate. The culture was grown in increasing concentrations of hydrolysate until the hydrolysate comprised 80% of the total media volume. Biomass production, substrate utilization, and ethanol production were evaluated. The adapted strain’s fermentation capabilities were considerably improved over the unadapted parent strain. On media containing 80% hydrolysate, the adapted strain produced a maximum of 4.5±0.04 g ethanol/L within 24 hours, using 91% of the available sugars. This resulted in an ethanol yield of 0.45±0.06 g/g. In contrast, the unadapted wild-type strain utilized less then 1% of the available sugars and produced no ethanol over a 72 hour period. The adapted strain was able to produce more biomass compared to the unadapted strain. The 80% adapted strain was also transferred to media containing lower percentages of hydrolysate (60 – 70%) and showed increased ethanol yields (+0.05-0.1 g/g) compared to strains that were only adapted to these levels. The increased productivity has not been lost with culture storage. Although more studies need to be conducted, these data support that adaption rather than acclimation has occurred. This strain performed more efficiently than previously reported P. stipitis adapted CBS 6054 strains. Adaptation is a useful and inexpensive means of optimizing organisms for the production of ethanol from lignocellulosic sugar mixtures.
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