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Flocculation and Expression of FLO Genes of a Saccharomyces cerevisiae Mezcal Strain with High Stress Tolerance

Israel Vergara-Álvarez1,2orcid tiny, Francisco Quiroz-Figueroa3orcid tiny, María Concepción Tamayo-Ordóñez1,4orcid tiny, Amanda Alejandra Oliva-Hernández1orcid tiny, Claudia Patricia Larralde-Corona1orcid tiny and José Alberto Narváez-Zapata1*orcid tiny



1National Polytechnic Institute (Instituto Politécnico Nacional), Center for Genomic Biotechnology, Blvd del Maestro s/n esq, Elías Piña Col. Narciso Mendoza, C.P. 88710, Reynosa (Tamaulipas), Mexico
2Aix-Marseille University, LCB (UMR7283), CNRS, Marseille, France
3National Polytechnic Institute (Instituto Politécnico Nacional), CIIDIR-IPN Unidad Sinaloa, Blvd. Juan de Dios Bátiz Paredes no. 250, Col. San Joachin, C.P. 81101 Guasave (Sinaloa), Mexico
4Genetic Engineering Laboratory, Department of Biotechnology, Faculty of Chemical Sciences, Autonomous University of Coahuila, Saltillo Unit, Mexico


Article history:
Received: 26 September 2018
Accepted: 8 November 2019
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Key words:
Saccharomyces cerevisiae, flocculation, stress tolerance, fermentation, mezcal, agave must


Mezcal is a distillate produced by spontaneous fermentation of the must obtained from stalks of Agave spp. plants that are cooked and pressed. Agave must contains a high amount of fructose and phenolic compounds, and fermentation usually occurs under stressful (and uncontrolled) environmental conditions. Yeasts capable of growing under such conditions usually display advantageous biological and industrial traits for stress tolerance such as flocculation. In this study, seven Saccharomyces cerevisiae strains isolated from mezcal must were exposed to temperatures ranging between 10 and 40 °C, and to different sugar sources (fructose or glucose). Yeasts grown in fructose increased their stress tolerance, determined by colony count in a microdrop assay, under low temperature (10 °C) compared to the growth at 40 °C on solid cultures. The most stress-tolerant mezcal strain (Sc3Y8) and a commercial wine (Fermichamp) strain, used as control, were grown under fermentation conditions and exposed to long-term temperature stress to determine their performance and their potential for flocculation. Compared to glucose, fermentation on fructose increased the metabolite accumulation at the end of culture, particularly at 40 °C, with 2.3, 1.3 and 3.4 times more glycerol (8.6 g/L), ethanol (43.6 g/L) and acetic acid (7.3 g/L), respectively. Using confocal microscopy analysis, we detected morphological changes such as aggregation and wall recognition at the level of budding scars in yeast, particularly in the Sc3Y8 strain when it was exposed to 40 °C. The analysis confirmed that this mezcal strain was positive for flocculation in the presence of Ca2+ ions. Analysis of FLO1FLO5 and FLO11 gene expression implicated in flocculation in both Saccharomyces strains showed a strong transcriptional induction, mainly of the FLO5 gene in the mezcal Sc3Y8 strain.

*Corresponding author: email2

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