Abstract
Distillery yeasts are poorly characterized physiological group among the Saccharomyces sensu stricto complex. As industrial yeasts are under constant environmental stress during fermentation processes and the nucleolus is a stress sensor, in the present study, nucleolus-related parameters were evaluated in 22 commercially available distillery yeast strains. Distillery yeasts were found to be a heterogeneous group with a variable content and length of rDNA and degree of nucleolus fragmentation. The levels of rDNA were negatively correlated with Nop1 (r = −0.59, p = 0.0038). Moreover, the protein levels of Sir transcriptional silencing complex and longevity regulators, namely Sir1, Sir2, Sir3 and Fob1, were studied and negative correlations between Sir2 and Nop1 (r = −0.45, p = 0.0332), and between Sir2 and Fob1 (r = −0.49, p = 0.0211) were revealed. In general, S. paradoxus group of distillery yeasts with higher rDNA pools and Sir2 level than S. bayanus group was found to be more tolerant to fermentation-associated stress stimuli, namely mild cold/heat stresses and KCl treatment. We postulate that rDNA state may be considered as a novel factor that may modulate a biotechnological process.
Highlights
The major role of the nucleolus is ribosome biogenesis, and other multiple functions have been assigned to the nucleolus (Boisvert et al 2007; Pederson 1998)
We have recently shown that rDNA acts as a genome buffer promoting chromosome homeostasis and regulates ethanol stress response in industrial yeast strains involved in winemaking and beer production (Deregowska et al 2015a)
We have reported that the genetic stability of analyzed distillery yeasts is promoted by the YRF1 gene copy number and strains with lower YRF1 gene dosage are more susceptible to DNA damage, especially in S. paradoxus group (Deregowska et al 2015b). rDNA is considered to be the most unstable region in the yeast genome being highly repetitive and prone to losing copies by homologous recombination among the repeats (Kobayashi 2008)
Summary
The major role of the nucleolus is ribosome biogenesis, and other multiple functions have been assigned to the nucleolus (Boisvert et al 2007; Pederson 1998). RDNA may promote genetic stability and regulate cellular stress response in industrially relevant yeast strains involved in winemaking and beer production (Deregowska et al 2015a) that suggests that nucleolus state is an important parameter during microbe-based industrial fermentations at harsh environmental conditions. Array-based comparative genomic hybridization (array CGH) analysis showed that the variabilities in the gene copy number and loci-specific gains and losses involved mainly the subtelomeric regions and naturally occurring diversity in the YRF1 (Y′ element ATP-dependent helicase) gene copy number may promote genetic stability in the S. bayanus group of distillery yeast strains (Deregowska et al 2015b). We have analyzed nucleolus parameters in 22 commercially available distillery yeast strains and revealed the relationships between rDNA pools, the levels of nucleolar protein Nop, Sir transcriptional silencing complex and longevity regulators, namely Sir1p, Sir2p, Sir3p and Fob1p and the tolerance to fermentation-associated stress stimuli. We postulate that rDNA state may be considered a novel parameter affecting yeast fermentation performance
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