Scientists engineer yeast to increase alcohol yield
doi:10.1038/nindia.2016.80 Published online 17 June 2016
In what may be a welcome news for breweries, scientists at National Institute of Plant Genome Research (NIPGR) in New Delhi have used a gene, isolated from a plant, to engineer the laboratory strain of the yeast Saccharomyces cerevisiae to boost alcohol yield.
S. cerevisiae, the common baker’s and brewer’s yeast used for fermentation of sugars into alcohol has a long association with the food and alcoholic beverage industries and production of bio-ethanol. In most of these industrial applications, after the fermentation is complete, the yeast cells are separated from the liquid for further processing of the fermented product.
To do this, the brewers use a process called 'flocculation' in which the yeast cells adhere to form 'clumps' that get separated out. The timing to initiate flocculation is crucial. Premature flocculation of yeast cells — before the sugar nutrient is depleted — hampers complete fermentation resulting in poor yield of alcohol, while delayed flocculation requires yeast cells to be removed by laborious and expensive procedures including centrifugation. A lot of efforts are being made to improve the process of flocculation.
"We found that the gene AtMed15 isolated from the model plant, Arabidopsis has the potential to be used as a tool to engineer yeast for robust flocculation and to increase ethanol production," Jitendra Thakur who led the research told Nature India. His team that included doctoral student Pradeep Dahiya and research associate Divya Bhat carried out a series of experiments to demonstrate the novel use of this gene.
Thakur said studies at his laboratory showed that over-expression of AtMed15 in yeast resulted in up-regulation of a set of 'flocculin' genes that are required for the process of flocculation. "As far as we know, this is the first report where a gene (AtMed15) from another kingdom (Arabidopsis) has been used to induce flocculation in yeast," he said.
The researchers found that the AtMed15 gene made yeast cells stickier and adhered strongly on the surface of the agar media, thereby showing 'robust flocculation' without affecting the growth. "The expression of AtMed15 in yeast actually increased the ethanol production (more than fourfold) during the course of cell growth and fermentation," the report said. Interestingly, the AtMed15-induced flocculation in yeast was unaffected by wide fluctuation of pH or temperatures "revealing its robust nature", another feature that makes AtMed15-driven flocculation suitable for exploitation in bioreactors.
"This strategy for increased ethanol production can be exploited for use in bio-ethanol production, and the brewery and beverage industries," the researchers say.
1. Dahiya, P. et al. Expression of AtMed15 of Arabidopsis in yeast causes flocculation and increases ethanol production in yeast culture. Sci. Rep. 6 (2016) doi: 10.1038/srep27967