title: Nitrogen source and mineral optimization enhance D: -xylose conversion to ethanol by the yeast Pichia stipitis NRRL Y-7124.
abstract: Nutrition-based strategies to optimize xylose to ethanol conversion by Pichia stipitis were identified in growing and stationary-phase cultures provided with a defined medium varied in nitrogen, vitamin, purine/pyrimidine, and mineral content via full or partial factorial designs. It is surprising to note that stationary-phase cultures were unable to ferment xylose (or glucose) to ethanol without the addition of a nitrogen source, such as amino acids. Ethanol accumulation increased with arginine, alanine, aspartic acid, glutamic acid, glycine, histidine, leucine, and tyrosine, but declined with isoleucine. Ethanol production from 150 g/l xylose was maximized (61+/-9 g/l) by providing C:N in the vicinity of approximately 57-126:1 and optimizing the combination of urea and amino acids to supply 40-80 % nitrogen from urea and 60-20 % from amino acids (casamino acids supplemented with tryptophan and cysteine). When either urea or amino acids were used as sole nitrogen source, ethanol accumulation dropped to 11 or 24 g/l, respectively, from the maximum of 46 g/l for the optimal nitrogen combination. The interaction of minerals with amino acids and/or urea was key to optimizing ethanol production by cells in both growing and stationary-phase cultures. In nongrowing cultures supplied with nitrogen as amino acids, ethanol concentration increased from 24 to 54 g/l with the addition of an optimized mineral supplement of Fe, Mn, Mg, Ca, Zn, and others.
authors: U. S. Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research, 1815 N. University Street, Peoria, IL 61604, USA. slininpj@ncaur.usda.gov
authors: Patricia J
authors: PJ
authors: Slininger
authors: Bruce S
authors: BS
authors: Dien
authors: Steven W
authors: SW
authors: Gorsich
authors: Zonglin L
authors: ZL
authors: Liu