Scientists from Duke University with colleagues from Brazil led by Lucas Argueso have analyzed the genome structures of bioethanol-producing microorganisms, uncovering genetic clues that will be critical in developing new technologies needed to implement production on a global scale.

Researchers at Stanford University and Brazilian colleagues led by Boris Stambuk and Gavin Sherlock have also analyzed the genome structure of industrial bioethanol yeasts, searching for variations in the number of gene copies in five strains employed in Brazil, including PE-2. Stambuk and colleagues found that all five industrial strains studied harbor amplifications of genes involved in the synthesis of vitamins B6 and B1 — compounds critical for efficient growth and utilization of sugar.

The two studies uncover genetic clues that will be critical in developing the new strains needed to increase production and use other crop sources.

Currently bioethanol is produced from the fermentation of plant material, such as sugar cane and corn, by the yeast Saccharomyces cerevisiae, just as in the production of alcoholic beverages. But the yeast strains thriving in the harsh conditions of industrial fuel ethanol production are much more hardy than their beverage brewing relatives, and surprisingly little is known about how these yeast were adapted to the industrial environment.

When researchers identify the genetic changes that underlie this adaptation, new yeast strains can be engineered to help shift bioethanol production into more crops and across more agricultural regions.

The two studies have been published in Genome Research and take a major steps toward this goal, identifying genomic properties of industrial fuel yeasts that likely gave rise to more robust strains.

Argueso’s group sequenced and analyzed the structure of the entire genome of strain PE-2, a prominent industrial strain in Brazil. The group’s work revealed that portions of the genome are plastic compared to other yeast strains, specifically the peripheral regions of chromosomes, where they observed a number of sequence rearrangements.  The chromosomal rearrangements in PE-2 amplified genes are involved in stress tolerance, which likely contributed to the adaptation of this strain to the industrial environment. As PE-2 is amenable to genetic engineering, the authors believe that their work on PE-2 will open the door to development of new technologies to boost bioethanol production.

Yeast Influenced by Oxygen and Temperature. Click image for more info.

Yeast Influenced by Oxygen and Temperature. Click image for more info.

Stambuk and Sherlock’s group experimentally demonstrated that the gene amplifications confer robust growth in industrial conditions, indicating that these yeasts likely adapted to limited availability of vitamins in the industrial process to gain a competitive advantage. The authors also suggest that this knowledge can be utilized to engineer new strains of yeast capable of even more efficient bioethanol production, from a wider range of agricultural stocks.

These two studies lay out the map of the yeasts genome to further study and closer examination.  Having the full genome is worthwhile in that the whole of the organism can be seen as it relates to the small genetic instructions.  Having the “map” speeds up things for other research.  Over time more parts of the metabolism will be understood thus allowing further engineering.

It’s in the engineering that the potential exists.  As the bioethanol business stands now only rich starch that easily converts to sugar or sugar itself are practical sources for processing material.  Yeast are unicellular fungi, a kind of single cell mushroom if you’ll allow the gross simplification. Other fungi have attributes in their genomes such that they consume the lignin and cellulose, although those are larger organisms.  The potential then exists, if only imaginary for now, that yeast can be engineered to consume other plant materials or other fungi could be engineered to produce ethanol or other alcohols.

But first you have to have the genome and understand it.  These two studies are the cornerstones of the coming growth in plant sources to renewable fuels.  Just as the population of humanity increases the population of the fungi are going to need to increase as well to digest civilizations wastes back into a natural cycle.

Population growth has out paced the adaptations of most of the rest of nature.  Fungi including yeast have an important role, more than just breaking down waste, but producing the fuels needed to keep modern life going.  The choice is more stark that most acknowledge, to have billions of people with standards of living worthy of being a good life, the of the rest of nature is going to need a helping hand in adapting into the planet’s carbon cycle.


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