Species Diversity And Ethanol Fermentation Characteristics Of Thermotolerant Yeasts

The aims of this study were to isolate and screen thermotolerant yeast,toinvestigate thermotolerant yeast diversity and their geographical distribution.Biophysical and biochemical characteristics and alcoholic fermentation ability wasmeasured in order to get strains which had a strong ability of fermentation to producealcohol at a high temperature.Sixty-four yeast strains that grow well at42℃were isolated from29fresh soilsamples.These strains were identified by large-subunit26S rDNA gene D1/D2domain sequencing and morphologic characteristic analysis.They were identified as7species,including C. tropicalis(39.1%of the total yeast strains),K. marxianus(23.4%),I. orientalis(29.7%),M. guilliermondii(1.6%),K.bovina(1.6%),C. palmioleophila(1.6%)and S. cerevisiae(3.1%).C. tropicalis is the dominant yeast strain, which was isolatedfrom a wide range of geographical distribution.I. orientalis and K. marxianus hadsecond quantity only to the C. tropicalis. Thermotolerant yeast strains mainlyphylogeneticly related to6genera.High temperature resistant ability was measured through solid agar medium. Thebest thermotolerant ability was detected in K. marxianus. Its maximum growthtemperature was50℃.Yeasts in different genus or different yeast strains in the samespecies showed different high temperature resistant ability.Alcohol resistance ability was also investigated through the Yeast ExtractPeptone Dextrose containing different concentrations of ethanol.I. orientalis showedthe strongest alcohol resistant ability at35℃,while K. marxianus had higher alcoholresistance compared with the other species at42℃and45℃.Their alcoholic fermentation was also investigated through glucose fermentationmedium. The isolated strains showed great difference in ethanol fermentation ability.The best ethanol fermentation ability was detected in K. marxianus6.5%(v/v)enthanol was produced in72h at40℃.K. marxianus has obvious advantages inethanol fermentation at high temperature.Alcoholic fermentation was investigated through glucose fermentation medium in15K. marxianus strains. KMBM2-5and KMBM1-2were got from the preliminaryscreening and the second screening experiment.5.13%（v/v）﹑4.96%（v/v）enthanolwas produced in72h at42℃and45℃through KMBM2-5.5.34%（v/v）、4.62%（v/v）enthanol was produced in72h at42℃and45℃through KMBM1-2.Their applicationdeserves further study.