GM yeast brews fuel from rubbish.

US researchers have used genetically modified yeast to enhance the production of biofuels from waste materials.

The new method solves some of the problems in using waste like straw to make bioethanol fuel.

The scientists involved say the development could help overcome reservations about using land for fuel production.

The research is published in the journal Nature Communications.


Many states around the world have plans to replace gasoline with bioethanol, but this has typically been by changing land-use from food crops to biofuel.

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We sort of rebuilt how yeast uses carbon”

Dr Jamie Cate University of California

Just this week, a representative of South Africa’s farming community announced that sorghum harvests would need to increase five fold to meet their government’s commitment to incorporate at least 2% bioethanol in petrol.

Sorghum is South Africa’s second biggest summer crop and is a staple food as well as being used in brewing and livestock feed.

However, scientists are now seeking more sustainable routes to generating biofuel – routes that would have a lighter impact on food prices and production.

Breakdown breakthrough

One is to consider using non-conventional plants such as seaweed. But among the most radical ideas is the suggestion that biowastes should be used to produce bioethanol, which is added to petrol replacing some fossil fuel.

“Wastes present a major opportunity in this respect. We have to start to think about wastes, such as sewage or landfill waste as resources – not problems to be disposed of,” Dr Gavin Collins, an environmental microbiologist at the National University of Ireland, Galway, told BBC News.

Using microbes to make fuel from biomass involves breaking down large complex biopolymer molecules.

These are indigestible to most bugs, and attempts to incorporate them into fuel production have slowed down the biotechnology, creating bottlenecks.

Biofuel boom.

Fuel plant

The European Union also has a declared aim that 10% of its transport energy should be from renewable sources, such as biofuels, by 2020.

To help meet this target, Europe’s largest biofuel plant opened this week at Crescentino, Italy.

It is designed to generate 75 million litres of ethanol a year from straw and a crop called Arundo donax, which can be grown on marginal land, and does not compete for resources with food.

One chemical that is produced when processing biowastes is a large sugar molecule called xylose.

When you try and use yeast to ferment xylose, rather than making alcohol for fuel directly, it generates acetic acid – essentially vinegar. This is poisonous to the yeast, and stops the fermentation.

Breaking down xylose and making acetic acid non-toxic are the two major problems that must be solved if biowastes such as straw are to be fermented to make fuel.

Now, US biotechnologists appear to have solved both problems, by developing a genetically engineered strain of yeast that simultaneously breaks down xylose and converts acetic acid to fuel.

“Xylose is a sugar; we can engineer yeast to ferment xylose,” said University of Illinois Prof Yong-Su Jin, one of the authors of the study.

“However, acetic acid is a toxic compound that kills yeast. That is one of the biggest problems in cellulosic ethanol production.”

The yeast digests the sugars in oxygen-poor conditions, making the process more efficient than digesters that rely on active mixing of air into the system.

Microbe driven

A new pathway, not yet discovered in nature, has been genetically engineered in the lab. This breakthrough means yeasts can be used much more efficiently to convert biowaste into biofuel.

“We sort of rebuilt how yeast uses carbon,” said principal investigator Dr Jamie Cate, of the University of California at Berkeley

One hurdle to implementing the discovery is that the new yeast that has been developed is genetically modified, and it is not yet clear how easily GM yeasts might be accepted for use on an industrial scale.

Dr Gavin Collins, however, remains upbeat about the prospects for biotechnology.

“We probably know the function of only about 0.01% of all living microbes on Earth,” he said.

“It may be that many of them can efficiently degrade even complex plant material and other wastes under anaerobic conditions. They may be present in nature but we haven’t found them yet.

“However, just look at what we have been able to do with the small fraction of microbes we understand – everything from antibiotic production; food and alcohol production; and biofuel production.

“Just think what we could do, or what we might discover, if we understood the function of just another 1%.”

Scientists Tweak Photosynthesis in Pursuit of a Better Biofuel.

For years researchers have been trying to figure out the best ways of making plants produce biofuels. But there is a funda­mental problem: photosynthesis, the process by which plants convert sunlight into stored chemical energy, is highly inefficient. Plants turn only 1 to 3 percent of sunlight into carbohydrates. That is one reason why so much land has to be devoted to growing corn for ethanol, among other bad biofuel ideas. And yet plants also have many advantages: they absorb carbon dioxide at low concen­trations directly from the atmosphere, and each plant cell can repair itself when damaged.

Scientists have begun a new effort to soup up photosynthesis and help humans make greener fuel. The U.S. Advanced Research Projects Agency for Energy, known as ARPA-e, has funded 10 such projects so far, most of which use genetic engineering to tweak a plant’s DNA-based instruction manual for growth, pigments, and the like. The largest grant—more than $6 million—has gone to the University of Florida to alter pine trees to make more turpentine, a potential fuel. Another project, led by Davis, Calif.–based Arcadia Biosciences, is aimed at inducing fast-growing grasses such as switchgrass to produce vegetable oil for the first time in history.

In the future, engineers might create a black plant that would absorb all incoming sunlight or a plant that uses different wavelengths of light to power the different steps of photo­synthesis; plants now use the same wavelengths for everything. An engineered biofuel-producing plant might even have smaller leaves, re­ducing its own energy demands for growth, or it might no longer store energy as sugar but turn it directly into a hydrocarbon molecule for human use as fuel.

The scientists in the program, dubbed PETRO, for plants engineered to replace oil, will also have to deal with the challenges of increasingly limited water supplies for crops and public skepticism of gen­etic­ally modified organ­isms. And they will face comp­etition from efforts to replace photosynthesis altogether, such as ARPA-e’s own Electrofuels program, which aims to induce microbes to make hydro­carbons, or from efforts to build artificial leaves that use the electricity from solar cells to split water into oxygen and hydro­gen for use as fuel. For plants, simply being green is no longer enough.

Source: Scientific American