In the long run, her persistence paid off.
In 1993, Dr. Ho’s Purdue group succeeded in the development of the world’s first genetically engineered yeast that could effectively ferment xylose to ethanol. In addition, her yeast, known as the Purdue Yeast, was also designed to effectively co-ferment a mixture of glucose and xylose together to ethanol, which is a crucial requirement for the efficient conversion of the major sugars present in cellulosic biomass. This was accomplished by cloning three modified genes, XR, XD, and XK that are important for converting xylose to ethanol in the yeast. This was the breakthrough, along with novel techniques for integrating the genes, that made it possible for yeast to co-ferment xylose with glucose to ethanol. The Purdue Group has continued to improve the Saccharomyces yeast with the goal of developing recombinant yeast ideally suited for large-scale industrial production of cellulosic ethanol. In particular, they have made the yeast extraordinarily stable. This was accomplished by developing a new integration method so that all the cloned genes could be integrated into the yeast chromosomes in high-copy-numbers.
Academic institutes, government laboratories, and ethanol producers including ADM (The Archer Daniels Midland Company – the world’s well known corn ethanol producer) have tested the Purdue yeast and validated its effectiveness in converting mixtures of glucose and xylose to ethanol from sugars in the crude hydrolysates of various types cellulosic biomass. In April 2004, Iogen, a Canadian cellulosic ethanol producer, began to use the Ho-Purdue yeast to produce ethanol from wheat straw in the world’s first production plant of its kind. In addition, Iogen has publicly acknowledged that the Ho-Purdue glucose and xylose-fermenting yeast is the most effective microorganism available for the production of ethanol from cellulosic materials (Purdue News release and ASM News letter, Oct 04, 2004).