Submitted to: Society of Industrial Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/25/2005
Publication Date: 8/21/2005
Citation: Slininger, P.J., Dien, B.S., Gorsich, S.W., Liu, Z. 2005. Mineral and nitrogen source optimization enhance d-xylose conversion to ethanol by the yeast Pichia stipitis [abstract]. Society of Industrial Microbiology Annual Meeting. Paper No. P07.
Technical Abstract: Efficient fermentation processes to produce ethanol from both the hexose and pentose sugars available in low-cost lignocellulosic biomass are sought to support the expansion of the biofuels industry. Pichia stipitis NRRL Y-7124 is a natural yeast able to convert xylose to ethanol, a capability not possessed by traditional Saccharomyces strains used to produce ethanol from corn starch. To investigate nutrition-based strategies for improving xylose to ethanol conversion by P. stipitis, kinetic studies were conducted on cultures provided a defined medium which was varied in nitrogen, vitamin, mineral, and purine/pyrimidine content. Vitamins, such as biotin, were confirmed to be required for growth and to improve ethanol production efficiency. Nitrogen source composition and mineral content had potentially greater impact than vitamins on the fermentation yield. When comparing culture media with and without additions of individual amino acids, ethanol accumulation significantly improved with added arginine, alanine, aspartic acid, glycine, histidine, leucine, proline, tyrosine, lysine, and methionine, but declined with added isoleucine. Of these, only proline, arginine and histidine significantly improved both ethanol and cell yields. Results further showed that ethanol production from 150 g/L xylose was significantly enhanced by optimizing the combination of urea and amino acids to supply 50-80% nitrogen from urea and 50-20% from casamino acids. When either urea or casamino acids was used as sole nitrogen source, ethanol accumulation dropped to 11 or 24 g/L, respectively, from the maximum of 53 g/L for the optimal nitrogen combination. Magnesium, iron, and zinc sulfates significantly improved ethanol production supported by casamino acids, urea, or their combination, while manganese chloride reduced it.