Team uses a cellulosic biofuels byproduct to increase ethanol yield

CHAMPAIGN, Ill. — Scientists report in Nature Communications that they have engineered yeast to consume acetic acid, a previously unwanted byproduct of the process of converting plant leaves, stems and other tissues into biofuels. The innovation increases ethanol yield from lignocellulosic sources by about 10 percent.

Lignocellulose is the fibrous material that makes up the structural tissues of plants. It is one of the most abundant raw materials on the planet and, because it is rich in carbon it is an attractive source of renewable biomass for biofuels production.

The yeast Saccharomyces cerevisiae is good at fermenting simple sugars (such as those found in corn kernels and sugarcane) to produce ethanol. But coaxing the yeast to feast on plant stems and leaves is not so easy. Doing it on an industrial scale requires a number of costly steps, one of which involves breaking down hemicellulose, a key component of lignocellulose.

“If we decompose hemicellulose, we obtain xylose and acetic acid,” said University of Illinois food science and human nutrition professor Yong-Su Jin, who led the research with principal investigator Jamie Cate, of the University of California at Berkeley and the Lawrence Berkeley National Laboratory. Jin and Cate are affiliates of the Energy Biosciences Institute (EBI), which funded the research. Jin also is an affiliate of the Institute for Genomic Biology at Illinois.

“Xylose is a sugar; we can engineer yeast to ferment xylose,” Jin said. “However, acetic acid is a toxic compound that kills yeast. That is one of the biggest problems in cellulosic ethanol production.”

In an earlier study, graduate student Soo Rin Kim (now an EBI fellow) engineered S. cerevisiae to more efficiently consume xylose. This improved ethanol output, but the process generated an excess of NADH, an electron-transfer molecule that is part of the energy currency of all cells. The buildup of acetic acid also killed off much of the yeast.

After discussing the problem with Jin, Cate had an idea – perhaps the team could induce the yeast to consume acetic acid. It later occurred to Jin that that process might also use up the surplus NADH from xylose metabolism.

By reviewing earlier studies, postdoctoral researcher Na Wei found that another organism, a bacterium, could consume acetic acid. She identified the enzymes that catalyzed this process and saw that one of them not only converted acetic acid into ethanol, but also would use the surplus NADH from xylose metabolism.

The team was not ready to start putting the genes into their yeast, however. They first had to determine whether their efforts were likely to succeed.

“One challenge with yeast is it has evolved to do one thing really well,” Cate said. “When you start adding these new modules into what it’s already doing, it’s not obvious that it’s going to work up front.”

To get a better idea of the feasibility of the idea, graduate student Josh Quarterman used computer simulations to see how adding the new genes to the yeast’s metabolic repertoire would affect its ethanol output. His calculations indicated that the pathway Wei had identified would boost ethanol production.

The new advance will streamline the fermentation process and will simplify plant breeding and pretreatment of the cellulose, the researchers say. The new advance will streamline the fermentation process and will simplify plant breeding and pretreatment of the cellulose, the researchers say.

Next, Wei did the painstaking work of inserting the desirable genes into the yeast, a process that took several months. When she tested the yeast, she saw that it produced about 10 percent more ethanol than before, in line with Quarterman’s calculations. In further experiments, she demonstrated that the new yeast was in fact making some of the ethanol from acetate, a first for S. cerevisiae.

“We sort of rebuilt how yeast uses carbon,” Cate said.

The breakthrough also will help those who focus on other steps in the biofuels production process, Jin said. Plant geneticists and those involved in pretreatment can stop worrying about finding ways to eliminate acetic acid from lignocellulose, he said.

“Many people are curious about why we don’t have cellulosic biofuel right now,” Jin said. “But it’s not because of one limiting step. We have many limiting steps in growing the biomass, storing, moving, harvesting, decomposing the biomass to the sugar, fermentation and then separation (of the ethanol). The advance that we are reporting involves one of those steps – fermentation. But it also will make other steps in the process a little easier.”

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University of Tennessee professor and student develop device to detect biodiesel contamination

The probability of contamination of diesel fuel is increasing as biodiesel becomes more popular and as distribution and supply systems use the same facilities to store and transport the 2 types of fuels

In 2010, a Cathay Pacific Airways plane was arriving in Hong Kong when the engine control thrusts seized up and it was forced to make a hard landing—injuring dozens. The potential culprit? Contaminated fuel.

The probability of contamination of diesel fuel is increasing as biodiesel becomes more popular and as distribution and supply systems use the same facilities to store and transport the two types of fuels.

A professor and student team at the University of Tennessee, Knoxville, has developed a quick and easy-to-use sensor that can detect trace amounts of biodiesel contamination in diesel.

The work of chemistry professor Ziling (Ben) Xue and doctoral student Jonathan Fong has been published in the journal Chemical Communications.

“The ability to detect biodiesel at various concentrations in diesel is an important goal in several industries,” said Xue. “There is particular concern over biodiesel contamination in jet fuel, because at higher levels it can impact the thermal stability and freezing point of jet fuel leading to deposits in the fuel system or gelling of the fuel. These issues can result in jet engine operability problems and possible engine flameout.”

Xue and Fong tested several dyes and found that the dye Nile blue chloride dissolved in alcohol, can be made into a thin film with high sensitivity toward biodiesel contamination in jet fuel. They tested small strips of the sensor and found it could successfully detect amounts of biodiesel contaminant in diesel as low as 0.5 parts per million—ten times below the allowable limit of 5 ppm in the U.S.—in less than 30 minutes.

With diesel, because it does not displace alcohol in the dye, the sensor remains blue. However, biodiesel replaces the alcohol, changing the sensor color to pink. This change can be seen with the naked eye.

“Right now, there is a dire need for quick, easy and direct detection of biodiesel in diesel and biodiesel-diesel blends to ensure safe and efficient-performing fuels,” said Fong. “The sensors we developed are intrinsically small, easy to use, inexpensive and can be mass produced for disposable applications”

The researchers say the sensor can be deployed in a portable reader for use in the field. The sensor can also be used for drivers delivering biodiesel-diesels to gas stations to quickly verify that the blends are accurate.

They are working with the UT Research Foundation to find partners to commercialize the technology.

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New possibilities for efficient biofuel production

Limited availability of fossil fuels stimulates the search for different energy resources. The use of biofuels is one of the alternatives. Sugars derived from the grain of agricultural crops can be used to produce biofuel but these crops occupy fertile soils needed for food and feed production. Fast growing plants such as poplar, eucalyptus, or various grass residues such as corn stover and sugarcane bagasse do not compete and can be a sustainable source for biofuel. An international collaboration of plant scientists from VIB and Ghent University (Belgium), the University of Dundee (UK), The James Hutton Institute (UK) and the University of Wisconsin (USA) identified a new gene in the biosynthetic pathway of lignin, a major component of plant secondary cell walls that limits the conversion of biomass to energy. These findings published online in this week’s issue of Science Express pave the way for new initiatives supporting a bio-based economy.

“This exciting, fundamental discovery provides an alternative pathway for altering lignin in plants and has the potential to greatly increase the efficiency of energy crop conversion for biofuels,” said Sally M. Benson, director of Stanford University’s Global Climate and Energy Project. “We have been so pleased to support this team of world leaders in lignin research and to see the highly successful outcome of these projects.” Lignin as a barrier

To understand how plant cells can deliver fuel or plastics, a basic knowledge of a plant’s cell wall is needed. A plant cell wall mainly consists of lignin and sugar molecules such as cellulose. Cellulose can be converted to glucose which can then be used in a classical fermentation process to produce alcohol, similar to beer or wine making. Lignin is a kind of cement that embeds the sugar molecules and thereby gives firmness to plants. Thanks to lignin, even very tall plants can maintain their upright stature. Unfortunately, lignin severely reduces the accessibility of sugar molecules for biofuel production. The lignin cement has to be removed via an energy-consuming and environmentally unfriendly process. Plants with a lower amount of lignin or with lignin that is easier to break down can be a real benefit for biofuel and bioplastics production. The same holds true for the paper industry that uses the cellulose fibres to produce paper.

A new enzyme

For many years researchers have been studying the lignin biosynthetic pathway in plants. Increasing insight into this process can lead to new strategies to improve the accessibility of the cellulose molecules. Using the model plant Arabidopsis thaliana, an international research collaboration between VIB and Ghent University (Belgium), the University of Dundee (UK), the James Hutton Institute (UK) and the University of Wisconsin (USA) has now identified a new enzyme in the lignin biosynthetic pathway. This enzyme, caffeoyl shikimate esterase (CSE), fulfils a central role in lignin biosynthesis. Knocking-out the CSE gene, resulted in 36% less lignin per gram of stem material. Additionally, the remaining lignin had an altered structure. As a result, the direct conversion of cellulose to glucose from un-pretreated plant biomass increased four-fold, from 18% in the control plants to 78% in the cse mutant plants.

These new insights, published this week online in Science Express, can now be used to screen natural populations of energy crops such as poplar, eucalyptus, switchgrass or other grass species for a non-functional CSE gene. Alternatively, the expression of CSE can be genetically engineered in energy crops. A reduced amount of lignin or an adapted lignin structure can contribute to a more efficient conversion of biomass to energy. This research was co-financed by the multidisciplinary research partnership ‘Biotechnology for a sustainable economy’ of Ghent University, the DOE Great Lakes Bioenergy Research Center and the ‘Global Climate and Energy Project’ (GCEP). Based at Stanford University, the Global Climate and Energy Project is a worldwide collaboration of premier research institutions and private industry that supports research on technologies that significantly reduce emissions of greenhouse gases, while meeting the world’s energy needs.

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Construction of E Cape bioethanol plant to start next year

Construction of a large-scale 90-million-litres bioethanol production facility is expected to start in the second quarter of next year, a Central Energy Fund (CEF) official said on Friday.

CEF biofuels project manager Sibusiso Ngubane stated that this project was a joint venture between State-owned financier, the Industrial Development Corporation (IDC), CEF, and Sugar Beet South Africa.
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Forecasting a change in technology: are Dye-sensitised Solar Cells a source of ubiquitous energy?


The purpose of this paper is to review developments in Dye-sensitised Solar Cells (DSC) and discuss the feasibility of the technology as a future source of ubiquitous energy. Rapid technological developments have made the technology a viable future photovoltaic technology, but its overall impact is still unclear. This review on recent developments strives, based on historical developments, to forecast the future for sensitised solar cells as a source of ubiquitous energy.
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Some relevant links on Dye-sensitised solar cells in Africa

Dye-ing To Power Solar Cells in Africa

Modification of charge transfer properties of TiO2 dye sensitized electrochemical solar cells

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