Identification and characterization of a thermotolerant yeast strain isolated from banana leaves

We have isolated a thermotolerant yeast strain, called TR2, from banana leaves and characterized it as Saccharomyces cerevisiae by sequencing about 25 kb at random, including structural genes and gene promoters. In all cases, the sequence identity was higher than 98%, and gene synteny was conserved. The strain is a homothallic diploid strain containing two sets of S. cerevisiae chromosomes that grows efficiently in a complete medium up to 40-41°C. We present a method allowing the isolation of stable haploid segregants. Analysis of the thermotolerance among the segregants proved to be complex, since we recovered more thermotolerant segregants than expected if the thermoresistance would had been conferred by a single gene. We obtained stable haploid segregants that were as thermotolerant as the original diploid strains. We also obtained a few thermosensitive segregants and strains that had an intermediate phenotype. The original TR2 strain or appropriate haploid derivatives can thus be used as safe probiotics in the food industry because of their rapid growth in a variety of conditions, such as high and low temperature, and their resistance to high salt concentrations.