Mutants of Pachysolen tannophilus showing enhanced rates of growth and ethanol formation from d-xylose

Mutants of Pachysolen tannophilus NRRL Y-2460 have been sought that show enhanced rates of d-xylose fermentation. Mutagenesis followed by enrichment in urea-xylitol broth generally resulted in a lower frequency of good ethanol producers than enrichment in nitrate-xylitol broth. Under aerobic conditions, the best xylose-fermenting strains (which were obtained from nitrate-xylitol broth) produced ethanol from xylose twice as fast and in 32% better yield than the parent strain. Under anaerobic conditions, these strains produced ethanol from xylose 50% faster than (but in the same yield as) the parent strain. These findings show that enrichment in nitrate-xylitol broth is a promising method for obtaining mutants of Pachysolen having enhanced fermentation rates.