Genetic modification of industrial Saccharomyces cerevisiae strain to improve ethanol production and conditional flocculation

Author(s)

Silvia Kazue Missawa

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2009-07-30

Examining board members

Gonçalo Amarante Guimarães Pereira; Jörg Kobarg; Flavio Henrique da Silva; André Ricardo Alcarde; Jorge Mauricio Costa Mondego

• Advisor: Gonçalo Amarante Guimarães Pereira; Anderson Ferreira da Cunha

Abstract

The increased need for replacing energy sources from fossil oil to renewable sources has prompted research initiatives throughout the world. Bioethanol is a highly competitive candidate to replace fuels such as gasoline. The production of Brazilian ethanol occurs by the fermentation of sugars from sugar cane juice by the yeast Saccharomyces cerevisiae. The industrial fermentation process used to produce ethanol fuel in Brazil includes a separation step by high-capacity centrifugation of the yeast cells after the exhaustion of the sugar, which makes the system complex and costly. In this work, laboratory and industrial yeast strains were transformed by genetic engineering techniques so that they are able to recognize the depletion of glucose from the medium and quickly separate by sedimentation, without the need of centrifugation. In order to reach this goal, plasmids and integrative cassettes were constructed using promoters sensitive to the presence of glucose in the environment regulating the expression of the genes that control flocculation. This genetic device promotes the formation of cellular aggregates that are separated from the medium by sedimentation only when glucose is depleted. Furthermore, it is reported in the literature that respiratory mutants produce a higher quantity of ethanol. Consequently, the PET191 gene was deleted in an industrial yeast strain; the gene product pet191 participates in the assembly of cytochome c, which is an essential component of the respiratory chain in these microorganisms. The deleted industrial strain JAY292 showed an increased production of ethanol by 4%. This percentage can be translated in an increase of more than 980 million liters of ethanol produced per year. These results are of great technological and industrial importance, and may contribute to the development of this strategic area for the country (AU)