Adaptive Laboratory Evolution for Multistress Tolerance, including Fermentability at High Glucose Concentrations in Thermotolerant <i>Candida tropicalis</i>
Koudkeo Phommachan,
Chansom Keo-oudone,
Mochamad Nurcholis,
Nookhao Vongvilaisak,
Mingkhuan Chanhming,
Vanhnavong Savanhnaly,
Somchanh Bounphanmy,
Minenosuke Matsutani,
Tomoyuki Kosaka,
Savitree Limtong,
Mamoru Yamada
Affiliations
Koudkeo Phommachan
Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi 753-8515, Japan
Chansom Keo-oudone
Department of Biology, Faculty of Natural Science, National University of Laos, Vientiane 7322, Laos
Mochamad Nurcholis
Department of Food Science and Technology, Faculty of Agricultural Technology, Brawijaya University, Malang 65145, Indonesia
Nookhao Vongvilaisak
Department of Biology, Faculty of Natural Science, National University of Laos, Vientiane 7322, Laos
Mingkhuan Chanhming
Department of Biology, Faculty of Natural Science, National University of Laos, Vientiane 7322, Laos
Vanhnavong Savanhnaly
Department of Biology, Faculty of Natural Science, National University of Laos, Vientiane 7322, Laos
Somchanh Bounphanmy
Department of Biology, Faculty of Natural Science, National University of Laos, Vientiane 7322, Laos
Minenosuke Matsutani
Department of Biological Chemistry, Faculty of Agriculture, Yamaguchi University, Yamaguchi 753-8515, Japan
Tomoyuki Kosaka
Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi 753-8515, Japan
Savitree Limtong
Department of Microbiology, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand
Mamoru Yamada
Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi 753-8515, Japan
Candida tropicalis, a xylose-fermenting yeast, has the potential for converting cellulosic biomass to ethanol. Thermotolerant C. tropicalis X-17, which was isolated in Laos, was subjected to repetitive long-term cultivation with a gradual increase in temperature (RLCGT) in the presence of a high concentration of glucose, which exposed cells to various stresses in addition to the high concentration of glucose and high temperatures. The resultant adapted strain demonstrated increased tolerance to ethanol, furfural and hydroxymethylfurfural at high temperatures and displayed improvement in fermentation ability at high glucose concentrations and xylose-fermenting ability. Transcriptome analysis revealed the up-regulation of a gene for a glucose transporter of the major facilitator superfamily and genes for stress response and cell wall proteins. Additionally, hydropathy analysis revealed that three genes for putative membrane proteins with multiple membrane-spanning segments were also up-regulated. From these findings, it can be inferred that the up-regulation of genes, including the gene for a glucose transporter, is responsible for the phenotype of the adaptive strain. This study revealed part of the mechanisms of fermentability at high glucose concentrations in C. tropicalis and the results of this study suggest that RLCGT is an effective procedure for improving multistress tolerance.
