Yeasts from peat in a tropical peat swamp forest in Thailand and their ability to produce ethanol, indole-3-acetic acid and extracellular enzymes

This study aimed to isolate and identify yeasts from peat in To Daeng peat swamp forest in southern of Thailand, and to investigate their ability to produce ethanol from glucose and xylose and to produce indole-3-acetic acid (IAA) and extracellular enzymes. A total of 65 yeast strains were obtained from 15 peat samples using an enrichment technique, and 61 strains were identified to be five species belonging to the phylum Ascomycota, namely Cyberlindnera subsufficiens, Debaryomyces fabryi, Meyerozyma guilliermondii, Saturnispora diversa and Schwanniomyces polymorphus var. africanus, and five species of the phylum Basidiomycota, namely Cryptococcus taiwanensis pro tem, Cutaneotrichosporon mucoides, Papiliotrema flavescens, Papiliotrema laurentii and Rhodotorula mucilaginosa. Four strains were unidentified and require further analysis. They differed from the type strain of P. flavescens by two nucleotide substitutions in the D1/D2 region of the LSU rRNA gene and nine nucleotide substitutions in the ITS region. R. mucilaginosa was the most prevalent yeast species, followed by S. polymorphus var. africanus, Cy. subsufficiens and D. fabryi. None of the yeast strains obtained in this study were able to ferment xylose to ethanol, but all ascomycetous yeast strains produced ethanol from glucose in a range of 9.0-58.0 g/L, with Cy. subsufficiens DMKU-YNB42-1 producing the highest ethanol concentration. Atotal of 62 strains produced IAA in a range of 9.0 to 66.9 mg/L, with the highest IAA produced by R. mucilaginosa DMKU-Y33-A. Investigation of the production of cellulases, xylanase, pectinase, amylase, protease and lipase revealed that all 65 yeast strains produced at least one extracellular enzyme, a lipase.