Characterization of thermotolerant, fermentative yeasts from hot spring drainage

Eight thermotolerant, ethanol-producing yeast strains were isolated from ho t spring drainage at Rendaiji in Shizuoka Prefecture. The tolerance to elev ated temperatures of three strains (RND13, 14 and 17) was studied in compar ison with that of mesophilic yeasts. All three grew on a liquid culture at temperatures up to 42-45 degreesC, with maximum growth rates at 37 degreesC or 35 degreesC, whereas the upper limit temperatures for fermentation were higher, ranging from 48 to 55 degreesC. Above all, RND13 had higher ethano l productivity of 72.1% at 40 degreesC for 24h than that of 57.0% obtained by brewers' yeast at 25 degreesC for 120 h. Regarding the taxonomy of RND13 , 14, and 17, they were found to be Toru-laspora delbrueckii, Dekkera sp., and Candida albicans, respectively. This is the first report on yeasts capa ble of fermentation over 51 degreesC, as well as on the isolation of yeasts from a hydrosphere with elevated temperatures.