Genetic and physiological alterations occurring in a yeast population continuously propagated at increasing temperatures with cell recycling

Abstract

This work investigated the effects of increasing temperature from 30°C to 47°C on the physiological and genetic characteristics of Saccharomyces cerevisiae strain 63M after continuous fermentation with cell recycling in a system of five reactors in series. Steady state was attained at 30°C, and then the temperature of the system was raised so it ranged from 35°C in the last reactor to 43°C in the first reactor or feeding reactor with a 2°C difference between reactors. After 15 days at steady state, the temperature was raised from 37°C to 45°C for 25 days at steady state, then from 39°C to 47°C for 20 days at steady state. Starter strain 63M was a hybrid strain constructed to have a MAT a/α, LYS/lys, URA/ura genotype. This hybrid yeast showed vigorous growth on plates at 40°C, weak growth at 41°C, positive assimilation of melibiose, positive fermentation of galactose, raffinose and sucrose. Of 156 isolates obtained from this system at the end of the fermentation process, only 17.3% showed the same characteristics as starter strain 63M. Alterations in mating type reaction and in utilization of raffinose, melibiose, and sucrose were identified. Only 1.9% of the isolates lost the ability to grow at 40°C. Isolates showing requirements for lysine and uracil were also obtained. In addition, cell survival was observed at 39-47°C, but no isolates showing growth above 41°C were obtained.

Enrichment of a continuous culture of Saccharomyces cerevisiae with the yeast Issatchenkia orientalis in the production of ethanol at increasing temperatures

“…As yeast strains tolerant to high temperatures can be of great value for biotechnological applications, it was decided to identify the elongated cells that were sporadically proliferating within a continuous fermentation system when temperatures as high as 39-47°C were reached within the bioreactors [34]. Based on this, it was concluded that this continuous system was capable of enriching its culture with yeasts able to grow at temperatures higher than those tolerated by conventional strains of S. cerevisiae.…”

“…Starter strain 63 M of Saccharomyces was the predominant isolate within the same fermentation system when operated at increasing temperatures. Due to the increasing temperatures, a great diversity of variants made up of haploid cells and recombinant and mutant strains of S. cerevisiae were obtained from this system [34].…”

“…Yeast isolates initially resembling non-Saccharomyces yeasts, as suggested by methods of the classical taxonomy, had their identiWcation conWrmed at the species level using RAPD-PCR. The majority of the yeast colonies that did not show positive growth on lysine medium were identiWed as resembling S. cerevisiae [34].…”

“…Alterations in physiological functions are strategically adopted by yeast cell populations in order to slow growth and consequently to reduce cell death as was observed in a Wve-stage fermentation system operating at increasing temperatures [34]. Gradual increases in temperature of this fermentation system give rise to favorable conditions for the enrichment of a culture with organisms that are more tolerant to thermal stress.…”

Saccharomyces cerevisiae strains associated with the production of cachaça: identification and characterization by traditional and molecular methods (PCR, PFGE and mtDNA-RFLP)

“…There have been many studies of the genetics of S. cerevisiae strains that are involved in the fermentation process for the production of wine (Blanco et al 2006;Nikolaou et al 2007;Vaudano and Garcia-Moruno 2008). Several molecular methods for identification of yeast strains, such as analysis of mitochondrial DNA (Fernández-Espinar et al 2001;Mercado et al 2007), karyotyping by pulsedfield gel electrophoresis (PFGE) (Cocolin et al 2004;Souza et al 2007;) and fingerprinting based on the repetitive delta sequences (Schüller et al 2004), have demonstrated a great deal of genetic diversity in oenological strains of S. cerevisiae (Nikolaou et al 2007), which is affected by factors that include geographical location (Guillamón et al 1996), technology used (Epifanio et al 1999) and temperature of fermentation (Fleet and Heard 1993;Vaudano and Garcia-Moruno 2008).…”