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Bioethanol is an organic compound resulted from the fermentation of sugar substrates by microorganisms which is used as alternative energy sources. During bioethanol fermentation yeast are exposed to various fermentation stresses, including temperature, osmotic, and oxidative stresess. Such conditions may decrease ethanol production. We previously isolated fermentation-stress tolerance yeast isolates from traditional Balinese beverages, identified as Wickerhamomyces anomalus BT2, BT5, and BT6. However no data available regarding the bioethanol production of those isolates. Our study indicates that these strains could utilize various sugar substrates (glucose, xylose, maltose, sucrose) in oxidative fermentative media. The highest value of substrate utilization efficiency following 48 hours fermentation was shown by BT6 on glucose (61.02%), BT 2 on xylose (55.44%) and maltose (60.90%). Measurement of ethanol production by Gas Chromatography showed that the strains were able to produce higher ethanol on the glucose substrate than other substrates. For instance, BT6 could produce the highest ethanol production (5.00 g/L) amongst strains tested by using glucose as substrate. Yet, the particular strains could only produce 0.30 g/L and 0.65 g/L by using xylose and maltose, respectively. For further genetic engineering purposes, we detected ADH1 gene from all three isolates, with high homology to the alcohol dehydrogenase from Saccharomyces cerevisiae, Geobacillus stearothermophilus and Pseudomonas aeruginosa. Further strain development can be carried out targeting the ADH1 gene, important for ethanol fermentation. [ABSTRACT FROM AUTHOR]

We previously developed ethanol-tolerant P. kudriavzevii R-T3 (P.ku R-T3) mutant from its parental strain P.ku R-WT by evolutionary adaptation method. Hence, we further analyze the ethanol productivity of the particular isolates in a monoculture and co-culture with industrial yeast Saccharomyces cerevisiae BY4741 at various inoculum ratio. Based on the spot assay, R3 mutant yeast showed better cell viability under 10% ethanol stress than the wild type, potentially due to the high expression level of PKINO1 gene involved in the synthesis of inositol. In the monoculture fermentation, S. cerevisiae could use glucose, while P.ku could use mixed glucose and xylose as carbon sources for ethanol fermentation. P.ku R-T3 performed the most potential ethanol kinetics parameters, including the highest ethanol production (10.10 g/L), ethanol productivity (0.21 g/L/h), and fermentation efficiency (84.36%). Upscaling the inoculum of P.ku R-T3 by ten times resulted in 10% higher ethanol production. However, the highest substrate utilization rate did not indicate an increase in ethanol production. Indeed, P.ku R-T3 showed a low mixed substrate use but produced higher ethanol production than S. cerevisiae, as much as 21-31%, depending on the initial inoculum. Interestingly, the coculture of P.ku R-T3 and BY4741 did not substantially produce higher ethanol production than the monoculture technique. About 30% reduction of ethanol production was found by co-culturing BY4741 with P.ku R-T3 than P.ku R-T3 alone. Taken together, the monoculture fermentation of P.ku R-T3 remains the promising fermentation technique than that of the co-culture with industrial yeast S. cerevisiae. [ABSTRACT FROM AUTHOR]