A University of Illinois (U of I) metabolic engineer has taken the first step towards the more efficient and economical production of biofuels by developing a strain of yeast with increased alcohol tolerance.
Biofuels are produced through the microbial fermentation of biomass crops, which yield alcohol-based fuels ethanol and iso-butanol if yeast is used as the microbe to convert sugars from biomass into biofuels.
‘At a certain concentration, the biofuels that are being created become toxic to the yeast used in making them,’ said Yong-Su Jin, an assistant professor of microbial genomics in the U of I Department of Food Science and Human Nutrition. ‘Our goal was to find a gene or genes that reduce this toxic effect.’
Jin worked with Saccharomyces cerevisiae, the microbe most often used in making ethanol, to identify four genes – namely MSN2, DOG1, HAL1 and INO1 – that improve tolerance to ethanol and iso-butanol when they are over-expressed.
’We expect these genes will serve as key components of a genetic toolbox for breeding yeast with high ethanol tolerance for efficient ethanol fermentation,’ he said.
To assess the over-expressed genes’ contribution to the components that have limited biofuel production, the scientists tested them in the presence of high concentrations of glucose (10 per cent), ethanol (five per cent) and iso-butanol (one per cent) and compared their performance with a control strain of Saccharomyces cerevisiae.
Over-expression of any of the four genes is said to have remarkably increased ethanol tolerance, but the strain in which INO1 was overexpressed elicited the highest ethanol yield and productivity – with increases of more than 70 per cent for ethanol volume and more than 340 per cent for ethanol tolerance when compared with the control strain.
According to Jin, the functions of the identified genes are very diverse and unrelated, which suggests that tolerance to high concentrations of iso-butanol and ethanol might involve the complex interactions of many genetic elements in yeast.
‘For example, some genes increase cellular viability at the expense of fermentation,’ he said. ’Others are more balanced between these two functions.’
Jin added: ‘Identification of these genes should enable us to produce transportation fuels from biomass more economically and efficiently. It’s a first step in understanding the cellular reaction that currently limits the production process.’
A further study of these genes should increase alcohol tolerance even further and this will translate into cost savings and greater efficiency during biofuel production, he said.