Further development of the cassette-based pYC plasmid system by incorporation of the dominant hph, nat and AUR1-C gene markers and the lacZ reporter system.

Dominant selection markers encoding hygromycin B phosphotransferase (hph), nourseothricin N-acetyltransferase (nat) and a mutant inositol phosphoceramide synthase (AUR1-C) were all incorporated into the pYC yeast plasmid vector system, thus expanding this system with possible alternatives to the use of G418 resistance. We found the markers to be of use not only in standard laboratory strains of Saccharomyces cerevisiae but also in an industrial strain of S. carlsbergensis (syn. of S. pastorianus) brewing yeast as well as in Saccharomyces kluyveri. As the pYC system contains means of counter-selection for plasmid loss and loop-out of integrated plasmids, it now provides ample opportunities for genetic manipulation of industrial and non-conventional yeasts when the URA3 marker and FOA counter-selection is not an option. Furthermore, the lacZ system for analyzing gene expression was included in the system.

The dynamics of the Saccharomyces carlsbergensis brewing yeast transcriptome during a production-scale lager beer fermentation.

The transcriptome of a lager brewing yeast (Saccharomyces carlsbergensis, syn. of S. pastorianus), was analysed at 12 different time points spanning a production-scale lager beer fermentation. Generally, the average expression rapidly increased and had a maximum value on day 2, then decreased as the sugar got consumed. Especially genes involved in protein and lipid biosynthesis or glycolysis were highly expressed during the beginning of the fermentation. Similarities as well as significant differences in expression profiles could be observed when comparing to a previous transcriptome analysis of a laboratory yeast grown in YPD. The regional distribution of various expression levels on the chromosomes appeared to be random or near-random and no reduction in expression near telomeres was observed.