The genome sequence of the Jean-Talon strain, an archeological tetraploid beer yeast from Québec

The genome sequences of archeological yeast isolates can reveal insights about the history of human baking, brewing and winemaking activities and migration around the globe. A yeast strain called Jean-Talon was recently isolated from the vaults of the Intendant’s Palace of Nouvelle France on a historical site in Québec City. This site has been occupied by various breweries, starting from the end of the 17th century and until the middle of the 20th century. We sequenced the genome of the Jean-Talon strain with short and long reads and reanalyzed the genomes of hundreds of yeast strains to identify its species of origin and determine how it relates to other domesticated and wild strains. The Jean-Talon strain is a tetraploid strain with numerous aneuploidies, is partially sterile and most closely related to beer strains from the beer and bakery genetic groups and industrial strains from the United Kingdom and Belgium. We conclude from this that the Jean-Talon strain most likely derives from recent brewing activities that took place in the same location and not from wild yeast that could have been domesticated by the original brewers of the Nouvelle France on the site.

A novel approach for the improvement of ethanol fermentation by Saccharomyces cerevisiae

Fermentation properties under the control of multiple genes are difficult to alter with traditional methods in Saccharomyces cerevisiae . Here, a novel genome engineering approach is developed to improve ethanol production in very high gravity fermentation with 300 g/L glucose as the carbon source. This strategy involved constructing aneuploid strains on the base of tetraploid cells. The tetraploid strain was constructed by using the plasmid YCplac33-GHK, which harbored the HO gene encoding the site-specific Ho endonucleases. The aneuploid strain, WT4-M, was selected and screened after the tetraploid cells were treated with methyl benzimidazole-2-yl-carbamate to induce loss of mitotic chromosomes. It was found that aneuploid strain WT4-M not only exhibited an increase in ethanol production and osmotic and thermal tolerance, but also an improvement in the sugar–ethanol conversion rate. Notably, WT4-M provided up to 9.8% improvement in ethanol production compared with the control strain. The results demonstrated that the strategy of aneuploidy was valuable for creating yeast strains with better fermentation characteristics.

VALEUR COMPETITIVE DES PLANTES AUTOTETRAPLOIDES D'ARABIDOPSIS THALIANA

In mixed cultures, an induced autotetraploid strain of Arabidopsis thaliana could supersede the original diploid. The fitness of these tetraploid plants was elucidated by comparing some factors acting on plant competition. The tetraploids were generally higher for seed germination and number of pods, but generally showed a later flowering and a lower seed number per pod. The whole balance was on behalf of the tetraploid strain. On the other hand the chromosome doubling did not impair the mitotic activity in Arabidopsis meristematic cells, and this fact may explain the growth and fitness of the tetraploid plants of that species.

Inaktivierungsversuche mit homozygoten Hefestämmen verschiedenen Ploidiegrades

A series of homozygous Saccharomyces-strains of different ploidy (haploid to tetraploid) has been bred. Except for the mating type alleles in the tri- and tetraploid strain the genomes of these strains are completely identical. The inactivation of these strains by UV, organic peroxides, X-rays (50 kV), 210Po-α-rays, accelerated He-, C- and O-nuclei was studied by avaluation of the ability to form macroscopic colonies. These different kinds of ionizing radiations cover a wide range of ionization density (LET). The triploid strain proved to be the most resistent one for each kind of radiation inactivation. A comparison of the RBE-values of the ionizing radiations showed a maximum at the LET-value of 1360 MeV cm2 g-1 (210Po-a-rays). It could be shown for diploid strains that a heterozygous condition in only the mating type alleles produces a remarkable resistance for X- and 210Po-α-rays. This effect, however, is absent in UV-inactivation.