Poster
Presentation 2-21
Co-fermentation
of Glucose and Xylose by Genetically Engineered
Haploid, Diploid and Tetraploid Saccharomyces cerevisiae Bearing Multiple Copies of
KDR Genes Cloned on High-Copy-Number Plasmid or Integrated into the Yeast
Chromosomes
Miroslav Sedlak,
Amit Mukerji and Nancy W.
Y. Ho*
Laboratory of Renewable Resources Engineering (LORRE)
Phone: (765)494-7046
Fax: (765)494-7046
E-mail: nwyho@ecn.purdue.edu
Cellulosic biomass is known to be an ideal raw
material for the production of chemicals by microbial processes, particularly
those produced in large volumes such as ethanol. However, cellulosic
biomass contains large amount of xylose in addition
to glucose. The naturally-occurring Saccharomyces
yeasts used for large-scale ethanol production from starch (glucose) cannot
metabolize xylose. In recent years, we have been able to
genetically engineer the Saccharomyces
yeasts to effectively co-metabolize glucose and xylose
both aerobically and anaerobically. This was accomplished by cloning and overexpressing three major xylose-metabolizing
genes - xylose reductase, xylitol dehydrogenase, and xylulokinase genes (KDR). The resulting genetically engineered yeast can
metabolize xylose aerobically and anaerobically
as well as effectively co-ferment both glucose and xylose
simultaneously to ethanol. First, these
three genes were cloned on a high copy number plasmid. Subsequently, we
developed an effective and reliable system for integrating multiple copies of
multiple genes into the yeast chromosome, and made it possible to effectively
integrate the three genes into the chromosomes of any Saccharomyces
yeast. In this paper, we compare the
ability of haploid, diploid and tetraploid S. cerevisiae with
identical genetic background to co-ferment glucose and xylose
when transformed with
multiple copies of KDR, either on high-copy-number plasmid or integrated on the
host chromosomes.