Early transcriptional response to biotic stress in mixed starter fermentations involving Saccharomyces cerevisiae and Torulaspora delbrueckii

Abstract

Advances in microbial wine biotechnology have led to the recent commercialization of several non-Saccharomyces starter cultures. These are intended to be used in either simultaneous or sequential inoculation with Saccharomyces cerevisiae. We analysed the transcriptional response to co-cultivation of S. cerevisiae and Torulaspora delbrueckii. The study is focused in the initial stages of wine fermentation with the goal of better understand the microbial interactions that can be stablished during wine fermentation with mixed-starters. Fermentations were carried out in bioreactors using synthetic grape must to mimic industrial conditions. Experiments were carried out in triplicate for fermentation kinetics, CO2 performance and RNAseq analysis. Both species showed a clear response to the presence of each other, even though the portion of the genome showing altered transcriptional levels was relatively small. Changes in the transcription pattern suggested a stimulation of metabolic activity and growth, as a consequence of the presence of competitors in the same medium. The response of S. cerevisiae seems to take place earlier, as compared to T. delbrueckii. Enhanced glycolytic activity of the mixed culture was confirmed by the CO2 production profile during these early stages of fermentation. Interestingly, HSP12 expression appeared induced by co-cultivation for both of S. cerevisiae and Torulaspora delbrueckii in the two time points studied. This might be related with a recently described role of Hsp12 in intercellular communication in yeast. Expression of S. cerevisiae PAU genes was also stimulated in mixed cultures.