Evaluation of new strategies for ethanol fermentation by Saccharomyces cerevisiae: gene expression analysis during bioelectric stimulus and selection of strains by high-throughput assays

Author(s)

Pedro Augusto Galvão Tizei

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2013-02-27

Examining board members

Gonçalo Amarante Guimarães Pereira; Luiz Carlos Basso; Renato Vicentini

• Advisor: Gonçalo Amarante Guimarães Pereira

Abstract

Fermentative ethanol production from substrates known as "first generation", such as sugar cane and corn starch, has reached very high levels of efficiency. The industrial strains used in these processes are already adapted to the industrial environment and possess characteristics that hinder further improvement by traditional genetic engineering. Two innovative approaches were used to seek more efficient fermentation processes: the use of bioelectric reactors to alter fermentation products and an evolutionary engineering assay to optimize heterologous phenotypes. Bioelectric fermentations were carried out with Saccharomyces cerevisiae, obtaining increases in ethanol productivity, without changing the final yield, and also changes in the proportions of byproducts glycerol and acetate. A distinct response was observed for an industrial strain cultivated under the same conditions. Global gene expression analyses were carried out for a laboratory and industrial strain under bioelectric stimulus. No changes were observed for the fermentative pathway, but there were large variations in expression for genes related to other aspects of yeast physiology, such as membrane lipid synthesis and unknown genes or genes with functions that are apparently unrelated to the fermentation process. A difference in the global response for the two strains was also evident. An automated method for evolutionary engineering assays was established, which allowed the selection of strains by growth on cellobiose. Using only the genetic variability present within the genome of a diploid industrial strain, it was possible to obtain haploid strains with superior growth rate when compared to the parental strain. Therefore, this strategy may be viable for obtaining superior phenotypes using distant strains of S. cerevisiae (AU)

• FAPESP's process: 10/02415-5 - Identification of the molecular mechanisms involved in the modulation of ethanol production by electric currents in Saccharomyces cerevisiae
• Grantee: Pedro Augusto Galvão Tizei
• Support Opportunities: Scholarships in Brazil - Master