Morphological, physiological, and molecular identification and characterization of yeast isolated from Indonesian fruits and woods

Yeast is one of important microorganisms in the biofuel industry in recent years. Identification and characterization of yeast are important for determining the quality and purity of yeast strains. This study intended to characterize yeast isolated from persimmon, special woods from Indonesia, and commercial yeast as a comparison. Macroscopic and microscopic morphological observation was performed to preliminarily identify the species of yeast isolates, supported with molecular characterization based on ITS fragment. The physiological aspect of yeast was assessed on their sensitivity to ethanol and a comparative experiment with glucose and sucrose substrate. A total of seven isolates were obtained. All yeast isolates had milky white color and slimy consistency, except for YK1.3 and YBK1, which had a watery consistency. Several isolates have oval and round shapes with blue color. All isolates were successfully sequenced based on the internal transcribed spacer (ITS) 1 and ITS4 regions. Homology analysis of the sequences against the GenBank database using BLASTN showed that seven isolates have homology with the Debaryomyces hansenii, Wickerhamomyces anomalus, Clavispora lusitaniae, and Metschnikowia agaves species. Physiologically, YRt2.1, YK1.3, YK2.2, and YK3.2 belonging to D. hansenii, C. lusitaniae, M. agaves, and W. anomalus, respectively, had better growth on glucose substrate incubated for 24 h. In contrast, YRt1.2, YB3.1, and YBK1 belonging to D. hansenii, W. anomalus, and D. hansenii, respectively, grew well on sucrose rather than glucose substrate. All isolates with glucose substrate seemed to be more tolerant to ethanol. Moreover, isolates YRT1.1 produced the highest ethanol concentration level until 39.28 ppm compared to the other isolates. This study clearly illustrates that identification based morphological and physiological characters as well as ITS fragment could be useful taxonomic tools for rapid identification at the species level of unknown isolated strains and constitutes a basis for initial yeast strain selection for future application in the production of ethanol.