P95: Identification and evaluation of genes involved in the mechanism of tolerance to ethanol of Zymomonas mobilis ZM4

In recent years, continuous growth in global population and industries has increased energy consumption, resulting in an energy crisis. Bioethanol has been considered and used as an alternative energy source. Among various ethanol-producing microbes, Zymomonas mobilis ZM4 has acquired special attention due to its higher ethanol yield and tolerance. Advances in genetic engineering are particularly important for the development of improved microorganisms in the production of ethanol, however, the variety of factors involved in the response to high concentrations of ethanol, makes it difficult to devise genetic engineering strategies to generate alcohol tolerant strains. Therefore we developed and characterized two Z. mobilis ZM4 derivative mutants (ER79ap and ER79ag) with higher ethanol tolerance obtained from a sequential transfer method with increments in ethanol concentration and in a fermentation of high density. Mutations carried by both mutants were identified by genomic sequencing. Strain ER79ap possesses three point mutations and also acquired the capacity to form small colonies. In contrast, strain ER79ag has four mutations and lost one of the plasmids present in ZM4. These mutants share one similar mutation. Description of point mutations, a physiological characterization of the mutants and a comparison with ZM4 will be presented.