Isolation and improvement of a thermotolerant Saccharomyces cerevisiae strain

The ambient temperature is a drawback in industrial ethanol production in J affna due to heat killing of yeast during fermentation. Thus a search was i nitiated for thermotolerant organisms suitable for fermentation in hot clim ates. The screening of the best wild-type organisms was undertaken as the f irst step. Thermotolerant strains were selected from environments where the re are chances of organisms being exposed to high temperature. The samples were enriched and screened for thermotolerant organisms which survived at 4 5 degreesC for 15 h. Among the yeast strains selected from different source s, thermotolerant strains with the capacity to withstand 45 degreesC for 15 h were found in samples collected from the compost heap and distillery env ironments. Three colonies from the distillery environment were selected for further studies and named p1, p2 and p3. Exponential phase (18 h) cultures of p1, p2 and p3 were subjected to 15 temperature treatment cycles (at 50 degreesC each for 3 h) and thermally adapted strains pt1, pt2 and pt3 were obtained, showing 100, 30 and 20% viability at 50 degreesC for 30 min respe ctively. The initial round of thermal adaptation cycles increased the durat ion of 100% viability from 20 h (p1) to 68 h (pt1) when incubated at 40 deg reesC. Very little benefit was obtained when pt1 was treated with u.v. and ethyl methanesulphonate. The selected strain was identified and designated as Saccharomyces cerevisiae S1. The ethanol produced from 100 g glucose l(- 1) by S. cerevisiae S1 was 46 g l(-1) (36 h), 38 g l(-1) (48 h) and 26 g l( -1) (48 h) at 40, 43 and 45 degreesC respectively in rich nutrient medium.