A system based rational approach to improve first and second generation bioethanol production by Saccharomyces Cerevisiae

There is a growing need for the use of renewable energies due to the steady increase in energy consumption, current dependence on fossil fuels to meet the growing energy demand, and the instability of the oil economy. Ethanol is mainly of interest because of its proven record as a fuel for land transportation. Saccharomyces cerevisiae is the preferred microbial cell factory for ethanol production. Bioethanol production by S. cerevisiae is currently the largest fermentation process in industrial biotechnology, and continuous efforts have been made to improve this process. Further progress could be achieved by developing optimized cell factories that can be used in industrial ethanol production. Moreover, the identification of sustainable substrates that can be used in productive and cost-effective processes is still a challenge in industry. The aim of this thesis was to develop new strategies to enhance first and second generation bioethanol production by S. cerevisiae. For this purpose, firstly, the suitability of five industrial S. cerevisiae strains for strain improvement studies were evaluated for their potential use in ethanol production processes. Moreover, utilization of by-products from agri-food industry by these strains was also investigated. Then, studies focused on ethanol stress, which is considered as one of the major stresses that yeast cells are exposed to during industrial ethanol production. For this, a novel network based approach was developed with the aim to find novel gene targets for rational design of ethanol tolerant S. cerevisiae strains, and the systems based information on transcriptome level was used for the identification of molecular mechanisms related to ethanol tolerance in S. cerevisiae. Finally, the global transcriptional response of a genetically engineered S. cerevisiae strain was also investigated with the aim of understanding the effect of the genetic modification, which confers wild-type cells with the ability of starch utilization. This study provides further evidence that system based approaches are powerful tools to understand and improve bioethanol production processes.