Thermo-and salt-tolerant Saccharomyces cerevisiae strains isolated from fermenting coconut toddy from Sri Lanka
‘Toddy’ is an alcoholic beverage obtained by the natural fermentation of phloem sap. We isolated 27 yeast strains from coconut toddy in Sri Lanka. Sequences of the 26S rDNA gene D1/D2 region from 18 strains showed 100% identity to Saccharomyces cerevisiae, while eight strains showed 99% identity to Pichia manshurica and a single isolate showed 99% identity to Saccharomycodes ludwigii. Regarding salt tolerance, all isolated strains of S. cerevisiae were found to grow in the presence of 10.0% (w/v) NaCl in yeast extract-peptone-dextrose (YPD), one of the isolates (SLY-10) grew even with 13.0% (w/v) NaCl. All the isolates grew well at 40 °C, and the 18 S. cerevisiae strains showed significant growth even at 42 °C. All the 18 S. cerevisiae strains still showed growth better than reference strains did in a medium with 7.5% (w/v) NaCl at 40 °C. All S. cerevisiae isolates produced relatively high alcohol concentrations than reference strains did when growing on batch-fermented media with 100 g·L−1glucose in at 40 °C. The five strains (SLY-3, SLY-4, SLY-8, SLY-9 and SLY-10) produced significant amounts of alcohol even at 45 °C: alcohol productivity over 24 h at 40 °C and 45 °C was similar in two different glucose concentrations, and the amount of produced alcohol was higher with 160 g·L−1 glucose than with 100 g·L−1glucose, significantly at 45 °C.
