Thanks to previous work funded by the National Institutes of Health, the team easily obtained Neurospora "knock-out" strains missing specific transporter genes and confirmed that, without all of them, the fungus could no longer eat cellodextrins as quickly.
"Most sugar-transporters let one sugar in at a time," Galazka said. "The sugar-transporters we found in Neurospora actually let in an entire chain of sugars. This means that four sugars can enter the fungus at once, if they are linked together.
Galazka subsequently created six strains of yeast, each with one extra gene from the Neurospora transporter family, along with a beta-glucosidase gene, also from Neurospora. The yeast strains produced Neurospora transporter proteins, and two of the strains were able to grow on cellodextrin as well as on glucose. One strain produced 60 percent more alcohol than normal yeast when grown on the two-glucose molecule, cellobiose.
Apparently, Galazka said, while normal yeast can't import cellodextrins or digest them once they're inside the cell, if they are given a Neurospora transporter and a beta-glucosidase from the fungus that stays inside the cells, it's able to do both.
"We've effectively made yeast more compatible with the enzymes used to break down woody plants," he said. "We think that the discovery of these transporters is a key step towards the efficient conversion of plant matter now considered waste into fuel."
"We now have to get these genes into industrial yeast strains the hearty, rock 'em, sock 'em yeast used commercially and get them to use more complicated plant material," Cate said.
He noted that a cellulosic process using yeast with transporter proteins could avoid having to add beta-glucosidases to the fermentation chamber, but enzymes would still be needed to break down cellulose into cellodextrins.
He and his colleagues are
|Contact: Robert Sanders|
University of California - Berkeley