Evolutionary Engineering for Improved Mixed-Pentose Utilization in Bioethanol-Yeast

An international group of scientists (from Sweden, Denmark and Portugal) reported the use of "evolutionary engineering" to improve the metabolic versatility of a strain of Saccharomyces cerevisiae, to effectively utilize mixed-pentoses for ethanol fermentation. Saccharomyces cerevisiae is the yeast that is commonly used for traditional fermentation of ethanol from glucose (a six-carbon sugar, or "hexose"). However, this yeast does not have a built-in metabolic capability to effectively utilize mixed-pentoses (5-carbon sugars, such as xylose and arabinose), which is abundantly present in lignocellulosic biomass after pretreatment. For such, it must be endowed with a metabolic versatility to utilize both hexoses and mixed-pentoses to ethanol. This would do much to increase "cellulose-ethanol" productivity and lower production cost.

The international scientific group was able to obtain an "evolved" strain of Saccharomyces cerevisiae with this metabolic versatility by using the tools of "evolutionary molecular biology". Also called, "evolutionary engineering", the technique reportedly "mimics" the process of natural evolution in living organisms (i.e. the "emergence of the best" from descendants), for obtaining desired biological traits. There are generally two steps in the technique: (1) the introduction of random mutations into a target gene to generate the variation, and (2) selection of the mutated genes that express products with a desired property under selective pressure. In the study, the scientists used a continuous culture technique under substrate limitation of xylose and arabinose, to implement selective pressure. Results showed that the evolved strain had increased consumption rates of the mixed-pentoses (xylose and arabinose), as well as an increase in the levels of pentose-utilization-associated enzyme activities. The full report is published in the open-access journal, Biotechnology for Biofuels (URL above).

Related information on evolutionary engineering:
http://www.ls.toyaku.ac.jp/~lcb-7/en/keywords/evolutionaryengineering.html
http://bs.kaist.ac.kr/~jsrhee/research03.html