Analysis of aging in lager brewing yeast during serial repitching

• Replicative aging of a brewing yeast strain during serial repitching was analyzed.
• Samples from 3 different breweries were studied.
• No increases in replicative age but stable rejuvenation rates were found.
• Yeast cells maintained longevity even after 7th run due to special gene regulation.
• Extended serial repitching is possible even under different culture conditions.

Serial repitching of brewing yeast inoculates is an important economic factor in the brewing industry, as their propagation is time and resource intensive. Here, we investigated whether replicative aging and/or the population distribution status changed during serial repitching in three different breweries with the same brewing yeast strain but different abiotic backgrounds and repitching regimes with varying numbers of reuses.Next to bud scar numbers the DNA content of the Saccharomyces pastorianus HEBRU cells was analyzed. Gene expression patterns were investigated using low-density microarrays with genes for aging, stress, storage compound metabolism and cell cycle.Two breweries showed a stable rejuvenation rate during serial repitching. In a third brewery the fraction of virgin cells varied, which could be explained with differing wort aeration rates. Furthermore, the number of bud scars per cell and cell size correlated in all 3 breweries throughout all runs. Transcriptome analyses revealed that from the 6th run on, mainly for the cells positive gene expression could be seen, for example up-regulation of trehalose and glycogen metabolism genes. Additionally, the cells’ settling in the cone was dependent on cell size, with the lowest and the uppermost cone layers showing the highest amount of dead cells.In general, cells do not progressively age during extended serial repitching.