Transcription analysis of S. cerevisiae in VHG fermentation: The genome-wide transcriptional response of Saccharomyces cerevisiae during very high gravity ethanol fermentations is highly affected by the stationary phase

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Abstract
Genome-wide expression was measured in a laboratory strain and an industrial strain of Saccharomyces cerevisiae which were grown batch-wise either at normal concentration (20 g/L glucose initially) or high substrate concentration (280 g/L maltodextrin initially) so-called very high gravity (VHG) fermentation. Simultaneous saccharification and fermentation (SSF) was applied in the VHG fermentations, using glucoamylase for the saccharification. The largest changes in transcription profiles within each strain were observed when comparing the stationary phase of the VHG fermentations with the growth phase in both VHG and standard medium fermentations. Furthermore, substantial differences between the two strains’ transcriptional response to VHG conditions were found. The industrial strain was found to be more stress-tolerant and to provide a more efficient fermentation in industrial medium than the laboratory strain. The transcriptional data profiles showed a higher number of stress-related genes upregulated in the industrial strain in stationary phase compared to the laboratory strain. Furthermore, strain differences in the regulation of HXT3, the upregulation of different maltose permeases in stationary phase (MAL11 in the laboratory strain, and MAL31 in the industrial strain) were found. Different regulation of ADH7 and GDH1 indicated that the industrial strain was provided with a better opportunity for redox balancing. In general, several differences were observed between the regulation of several genes and their actual database description, which indicated that results from the S. cerevisiae S288C strain are not necessarily representative for other strains and at other cultivation conditions than standard medium.