Genetic engineering of Brazilian industrial strain Barra Grande for xylose fermentation

Abstract

The increased energy demand and the consensus on the need to reduce emissions of greenhouse gases and dependence on fossil fuels is driving the development and improvement of biofuels production. Nowadays, ethanol is the most widely used biofuel, but to attend the global, efforts are being made to increase its production, and one of the options is the second generation ethanol (2GE) production. The 2GE ethanol is produced through the fermentation of sugars released from complex polysaccharides, in Brazil sugarcane bagasse is the biomass of choice. However, for 2GE production is necessary overcome several challenges, such as the use of all fermentable sugars released from the biomass degradation. Since Saccharomyces cerevisiae is not able to ferment pentose, the 2GE production will not be economically viable if these sugars (especially xylose) were not ferment in addition to glucose. Thus, this project has as main goal the construction of a xylose fermenting yeast strain derived from the industrial strain S. cerevisiae Barra Grande (BG-1).Using evolutionary adaptation is expect that this strain will be able to resistant to inhibitory components present in liquor C5. This project is innovator since it will be the first time that this Brazilian strain will be genetically modified to ferment efficiently xylose, using the CRISPR-Cas system, that allows quickly and precise modifications. Besides, it is proposed the expression of acetate consumption pathway, and evolutionary engineering of the strain in media with xylose as carbon source and liquor C5 derived of bagasse. The ethanol yield and productivity will be evaluated on semi-industrial bioreactors. Additionally, genomic and transcriptomics studies are proposed, to better understand the metabolism of the strains during the fermentation process. Although several research groups in Brazil, and especially abroad, have been working on that, there is no microorganism, adapted to Brazilian fermentation conditions, capable of use xylose / liquor for the E2G production with similar yield and productivity to that obtained with glucose / sucrose. Thus, this proposal is extremely promising since can generate a new technology of socio-economic and environmental interests, being fundamental for the Brazilian sugar-energy sector. (AU)