Researchers Sequence Genome of Sugarcane Ethanol Yeast; Potential for Cellulosic Ethanol

14 October 2009

Researchers from Duke University Medical Center, the University of North Carolina, and Brazil have sequenced the genome of PE-2, a strain of the yeast Saccharomyces cerevisiae that thrives on turning sugarcane into ethanol. An open access paper on the work was published in the journal Genome Research.

When oil prices rose to new highs in the 1970s, Brazil invested in ethanol created from the its sugar cane crops. Commercially available baker’s yeast was used to break down the sugar cane into ethanol, but genetic tests showed that this yeast quickly disappeared in the harsh environment of industrial fermentation vats. However, a yeast that grows naturally on the sugar cane was still viable in the vats and lasted through many more generations: PE-2.

Understanding this microbe may enable more efficient biofuel production, and also will produce even more robust industrial organisms that are versatile and capable of producing advanced biofuels from non-food crops like switchgrass.

We took an organism that is hugely important from an industrial standpoint but completely unknown in terms of its genetic and molecular properties. We learned much more about how a complex genome is organized and may contribute to a robust and well-adapted organism. Now we have sequenced the genome, so we have a road map that will allow us to build upon its natural abilities. This opens the door to crossing yeast strains to make even more efficient yeasts for enhanced biofuel production.

—Lucas Argueso

Argueso said the PE-2 genome will aid research into finding the best and strongest yeasts for converting the cellulose in grasses into biofuel, Argueso said.

I believe this strain has a natural talent for carbohydrate biofuels that have not yet been introduced in the United States. When the technology is engineered to effectively break down cellulose, I believe this strain of yeast will be an ideal delivery vehicle for that technology.

—Lucas Argueso

The study also yielded some interesting genetic information about Saccharomyces cerevisiae, the most studied and utilized yeast species. The paper suggests that industrial yeast strains may have a high rate of evolution, helping them adapt to the stressful conditions of batch fermentation, said Tom Petes, senior author and professor of molecular genetics and microbiology at Duke University.

PE-2 yeast are diploid, having two copies each of 16 different chromosomes. In the case of these yeast, the genetic structure lends itself to robust life, Petes says, because the two copies of each chromosome are slightly different. The greatest differences between paired chromosomes occur at the ends of the structures, making reconfiguration easier and speeding adaptation to evolve.

The study was funded by two grants from the National Institutes of Health, a BRASKEM/FAPESP grant, and support from ETH Bioenergia, a Brazilian company that produces ethanol and sugar from sugar cane.

Other authors include Margaret Dominska and John H. McCusker, of the Duke Department of Molecular Genetics and Microbiology; Fred S. Dietrich, also of the Department of Molecular Genetics and Microbiology and the Duke Institute for Genome Sciences and Policy; and Piotr A. Mieczkowski, of the Department of Genetics at the University of North Carolina, Chapel Hill. Brazilian scientists also played key roles in the study, including Gonçalo A.G. Pereira, Marcelo F. Carazzolle, Fabiana M. Duarte, Osmar V.C. Netto, Silvia K. Missawa, Felipe Galzerani, Gustavo G.L. Costa, Ramon O. Vidal, Melline F. Noronha, Anderson F. Cunha, Maria G.S. Andrietta and Sílvio R. Andrietta of Campinas State University; and Luiz H. Gomes, Flavio C.A. Tavares, and André R. Alcarde, of the University of São Paulo.

Resources

• Juan Lucas Argueso et al. (2009). Genome structure of a Saccharomyces cerevisiae strain widely used in bioethanol production. Genome Res. doi: 10.1101/gr.091777.109