Cornstalks, wheat straw and other crop residues may soon be less expensive to convert into cellulosic ethanol, thanks to a new biorefinery yeast discovered by scientists at the USDA-ARS National Center for Agricultural Utilization Research in Peoria, IL.

The yeast – Saccharomyces cerevisiae strain NRRL Y-50049 – successfully ferments plant sugars into cellulosic ethanol despite interference by problematic compounds such as furfural and HMF in fermenters, says molecular biologist Zonglin Lewis Liu.

The troublesome compounds, created during dilute acid pretreatment of the crop residues, inhibit yeast growth and reduce ethanol yields. In particular, they damage yeast cell walls and membranes, disrupt yeast genetic material such as DNA and RNA and interfere with yeast enzymes' fermentation abilities.

In research that began in 2003, Liu and coworkers have worked with dozens of strains of S. cerevisiae, a species already used to make ethanol from plant starch. Using a laboratory approach known as evolutionary engineering, the scientists speeded up the microbe's natural adaptation to the hostile environment created by the compounds. NRRL Y-50049 was one result of these studies.

The scientists are discovering more about the genes and the multiple networks of genes that are likely responsible for the notable tolerance that this yeast has shown in lab tests.

Their research suggests that, of the nearly 7,000 genes in the S. cerevisiae genome, more than 350 may be involved in counteracting stress. For instance, Liu and colleagues determined that a gene called YAP1 acts as a master gene, orchestrating interactions of many related genes so that they work together to reduce the impact of furfural and HMF.

Read more about this research in the August issue of Agricultural Research magazine.