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10/10/2013 Making use of biofuel waste Yeast engineered to eat acetic acid Richard Jansen US RESEARCHERS have engineered a strain of yeast that will consume unwanted by-products made when plant stems and leaves are converted into biofuels. The team, based at the University of Illinois, says that discovery could improve the ethanol yield from lignocellulosic sources by as much as 10%. The yeast used to produce ethanol from lignocellulosic sources, Saccharomyces cerevisiae , is good at fermenting simple sugars – such as those found in corn kernels and sugarcane – to produce ethanol.  However, coaxing the yeast into eating the 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,” says Illinois food science and human nutrition professor Yong-Su Jin, who helped lead the research. “Xylose is a sugar; we can engineer yeast to ferment xylose,” he continues. “However, acetic acid is a toxic compound that kills yeast. That is one of the biggest problems in cellulosic ethanol production.” The researchers came up with a plan to deal with the waste after finding another organism – a bacterium – that consumed acetic acid. They isolated the genes responsible for the process, and began inserting them into the yeast. “One challenge with yeast is it has evolved to do one thing really well,” says Jamie Cate, from the University of California at Berkeley, who also helped direct the research. “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.” “We sort of rebuilt how yeast uses carbon,” he adds. As well as those carrying out the conversion process, Jin claims that the breakthrough will also help those who focus on other steps in biofuels production. Plant geneticists and those involved in pretreatment can stop worrying about finding ways to eliminate acetic acid from lignocelluloses, for example. “Many people are curious about why we don’t have cellulosic biofuel right now,” he continues. “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. “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.” Continue reading →