Isolation and Characterization of a Non-Saccharomyces Yeast with Improved Functional Characteristics for Ethanol Production

Aim: To isolate a thermotolerant yeast strain with fermentation potential at elevated temperatures.

Study Design: Lab experimental design was used in the study.

Methodology: Yeasts were isolated from over-ripened fruits and naturally fermenting sugarcane juice. Four isolates showing relatively higher fermentation ability were screened for their fermentation potential. The selected strain was tested for its thermotolerance, osmotolence as well as to work at varied pH.

Results: Isolate Y-4 produced relatively higher ethanol than the other isolates from 15 gl-1 glucose. Scanning electron micrographs (SEM) of isolate Y-4 showed oval to spherical cells with diameter ranging from 4.5 to 6.2 µm. On the basis of the SEM images and 28s rRNA gene sequencing, isolate Y-4 was identified as Pichia kudriavzevii and designated as P. kudriavzevii SK1. P. kudriavzevii SK1 metabolized glucose, galactose, mannose, maltose and fructose. It showed the potential to grow at a glucose concentration of 300 gl-1 and ferment at 45°C, though the best results were obtained from 15-20 gl-1 glucose at 35°C. Reference strain Saccharomyces cerevisiae MTCC 11815 produced low concentrations of ethanol under similar conditions. With 200 gl-1 initial glucose concentration 86.1 and 87.9 gl-1 ethanol was obtained in shake flasks and laboratory batch fermenter experiments, respectively at pH 5 at 35°C. This study revealed that P. kudriavzevii SK1 could be utilized for pilot scale fermentation for high gravity fermentations.