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article imageEssential Science: Bio-designing yeast to improve biofuels

By Tim Sandle     Feb 15, 2016 in Science
Scientists have engineered a new strain of yeast designed to create biofuel from switchgrass, turning the collected cellulosic biomass into an energy alternative. The process is described together with a review of biofuel progress.
Biofuels are much spoken about as the next generation energy source for vehicles and many industrial applications. So far, the full realization of that potential has been hampered by discovering the right types of microorganisms and imperfections with the process of making biofuel, which hampers the yield.
Biofuel refers to a fuel produced through a biological process, as opposed to fuels created through geological processes as with petroleum. There are different types of biofuels and different types of microorganisms — algae, fungi (yeasts and filamentous) and bacteria — are involved in the different production processes. Another variation is with the source material. Where plant matter is used (as the basis of the 'biomass'), it is not only the type of plant that is important; different efficiencies even go as far down as the arrangement of the molecules in plant cell walls.
An example of a biofuel is bioethanol. This is a form of alcohol manufactured by fermentation. Bioethanol is derived mostly from carbohydrates produced in sugar or starch crops such as corn, sugarcane, or sweet sorghum. The process requires an enzyme catalyst, and this is produced by a microorganism. Bioethanol is either used directly as fuel or as an additive to other fuels (added to gasoline, it increases the octane level and improves vehicle emissions.)
An alternative to the production of alcohol, is where hydrocarbons are produced as the basis of the biofuel. This is the case with biodiesel. Most biodiesels are made from vegetable oil.
One of the problems with creating biofuels like bioethanol is the solvent needed to break down the biomass can hinder the next step of the process: fermentation. This is where the new research comes.
Scientists working at the Great Lakes Bioenergy Research Center (GLBRC), which is part of the University of Wisconsin-Madison, have developed a new strain of yeast that should improve the efficiency of making fuel from cellulosic biomass derived from switchgrass (Panicum virgatum.) Yeast are single-celled microorganisms that are classified, along with molds and mushrooms, as members of the Kingdom Fungi. Switchgrass is a perennial warm season bunchgrass native to North America.
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast  having been ins...
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to winemaking, baking, and brewing fro a 1000 years.
Douglas Smith
The new yeast is designed to overcome a conundrum with biofuels production: solvents are needed to break down different kinds of biomass (polysaccharides) into different components — simpler sugars. The simpler sugars are then fermented to produce liquid biofuels, with the yeast acting as an enzyme.
However, the residuals from the solvents are often which toxic to the microorganisms needed to ferment the deconstructed products into fuel. This either means expensive processes to remove traces of the solvents or reduced efficiency of the microbial fermentation process.
The solution to the scientists was to focus on the microorganism. They used chemical genomics to genetically engineer a yeast that was resistant to solvent residues. This was achieved by identifying which genes made a yeast susceptible to the solvent and then deleting them.
A biomass generating plant.
A biomass generating plant.
Lead researcher, Quinn Dickinson stated in a research note: "What this work shows more broadly is that we can use chemical genomics to rapidly design new yeast strains in response to any new chemical compound, or any new solvent used as part of a new bioconversion technology."
The bio-design method developed not only created the new type of yeast, the process was in and of itself novel and could have other applications where the genetic modification of microorganisms is required. The research has yet to be published in a peer reviewed journal, although such a paper is being prepared.
There are several ethical questions associated with the use biofuels. For example, are they a a sustainable energy supply or a product harmful to the environment? Is it a problem that some of the crops used to produce biofuels undergo gene modification? With the microorganisms used, some of these are tweaked and patented. This raises questions of exactly how a company has the rights to a microorganism not dissimilar to those found in nature.
To add to these dilemmas: Does the production of biofuels, in terms of the need for cellulose, take away plants that could be better served as crops to feed the world's poor? Some crops used in biofuel production are non-food, such as oilseed, whereas others are plants that could be (or were) used to produce food. There are 'greener' alternatives. For example, the company Celtic Renewables has produced the alcohol biobutanol from draff — the sugar-rich kernels of barley which are soaked in water to facilitate the fermentation process necessary for whisky production — and pot ale, the yeasty liquid that is heated during distillation.
These are not easy questions to answer, but they highlight the fact that the biofuel science is not politically neutral.
This article is one of Digital Journal's Essential Science columns. Each week we explore a topical and important scientific issue. Last week we explored the latest medical studies for tackling concussion and head injuries; and the week before we tackled space exploration by asking why are strong bones are needed for space travel?
More about Biofuels, Energy, Yeast, Microbiology, Biomass
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