Selection and Adaptation of Saccharomyces cerevisae to Increased Ethanol Tolerance and Production

Abstract

A total of 24 yeast strains were tested for their capacity to produce ethanol, and of these, 8 were characterized by the best ethanol yields (73.11-8 1.78%). The most active mutant Saccharomyce s cerevisiae ER-A, resistant to ethanol stress, was characterized by high resistance to acidic (pH 1.0 and 2.0), oxidative (1 and 2% of H2O2), and high temperature (45 and 52 degrees C) stresses. During cultivation under all stress conditions, the mutants showed a considerably increased viability ranging widely from about 1.04 to 3.94-fold in comparison with the parent strain S. cerevisiae ER. At an initial sucrose concentration of 150 g/l in basal medium A containing yeast extract and mineral salts, at 300C and within 72 h, the most active strain, S. cerevisiae ER-A, reached an ethanol concentration of 80 g/1, ethanol productivity of 1.1 g/Il/h, and an ethanol yield (% of theoretical) of 99.13. Those values were significantly higher in comparison with parent strain (ethanol concentration 71 g/1 and productivity of 0,99 g/l/h). The present study seems to confirm the high effectiveness of selection of ethanol-resistant yeast strains by adaptation to high ethanol concentrations, for increased ethanol production.

Improvement of ethanol production by ethanol-tolerant Saccharomyces cerevisiae UVNR56

“…Viable cell counts of UVNR56 were significantly higher than the wild-type, but its viability was lower compared to the no added ethanol conditions (Figure 2 b). Several studies have shown that an improvement in ethanol tolerance leads to an increase in both ethanol productivity and yield (Basso et al 2008 ; Fiedurek et al 2011 ; Hou 2009 ). As expected, we found a correlation between cell viability and fermentation capability.…”

“…In the ethanol industry, ethanol production is usually among 10-14% (v/v) and the theoretical yield has to be as high as 90-93% of the fermentation efficiency for the conversion of glucose into ethanol (Bai et al 2008 ). Consequently, several studies to date have focused interest on ethanol tolerance of ethanol-producing yeasts based on the presumption that ethanol-tolerant yeast strains would have enhanced ethanol productivities and yields (Fiedurek et al 2011 : Shi et al 2009 ; Thammasittirong et al 2012 ).…”

Strain improvement of industrially important microorganisms based on resistance to toxic metabolites and abiotic stress

“…cerevisiae strain ER‐A reached an ethanol concentration of 80 g/L, ethanol productivity of 1.1 g/L/h, and ethanol yield (% of theoretical) of 99.26, which were significantly higher in comparison with the parent strain (ethanol concentration 58 g/L and productivity of 0.8 g/L/h). The studies seem to confirm a highly effective selection of yeast strains resistant to high ethanol concentrations by adaptation .…”

“…Considerably increased viability occurred in mutants during cultivation under all stress conditions, the level of which ranged widely from about 1.04 to 3.94‐fold in comparison with the parent strain S . cerevisiae ER .…”

“…These include osmotic pressure imposed by a high initial sugar concentration and stress induced by fermentation end‐products or sub‐products such as ethanol or acetate. However, the stress induced by an increasing ethanol concentration up to toxic levels during ethanolic fermentation is responsible for reduced ethanol production yields, and eventually, for stuck fermentations . Thus, yeast strains that can endure stress imposed by high ethanol concentrations are highly desired.…”