<it>Starmerella bombicola </it>influences the metabolism of <it>Saccharomyces cerevisiae </it>at pyruvate decarboxylase and alcohol dehydrogenase level during mixed wine fermentation

<p>Abstract</p> <p>Background</p> <p>The use of a multistarter fermentation process with <it>Saccharomyces cerevisiae </it>and non-<it>Saccharomyces </it>wine yeasts has been proposed to simulate natural must fermentation and to confer greater complexity and specificity to wine. In this context, the combined use of <it>S. cerevisiae </it>and immobilized <it>Starmerella bombicola </it>cells (formerly <it>Candida stellata</it>) was assayed to enhance glycerol concentration, reduce ethanol content and to improve the analytical composition of wine. In order to investigate yeast metabolic interaction during controlled mixed fermentation and to evaluate the influence of <it>S. bombicola </it>on <it>S. cerevisiae</it>, the gene expression and enzymatic activity of two key enzymes of the alcoholic fermentation pathway such as pyruvate decarboxylase (Pdc1) and alcohol dehydrogenase (Adh1) were studied.</p> <p>Results</p> <p>The presence of <it>S. bombicola </it>immobilized cells in a mixed fermentation trial confirmed an increase in fermentation rate, a combined consumption of glucose and fructose, an increase in glycerol and a reduction in the production of ethanol as well as a modification in the fermentation of by products. The alcoholic fermentation of <it>S. cerevisiae </it>was also influenced by <it>S. bombicola </it>immobilized cells. Indeed, Pdc1 activity in mixed fermentation was lower than that exhibited in pure culture while Adh1 activity showed an opposite behavior. The expression of both <it>PDC1 </it>and <it>ADH1 </it>genes was highly induced at the initial phase of fermentation. The expression level of <it>PDC1 </it>at the end of fermentation was much higher in pure culture while <it>ADH1 </it>level was similar in both pure and mixed fermentations.</p> <p>Conclusion</p> <p>In mixed fermentation, <it>S. bombicola </it>immobilized cells greatly affected the fermentation behavior of <it>S. cerevisiae </it>and the analytical composition of wine. The influence of <it>S. bombicola </it>on <it>S. cerevisiae </it>was not limited to a simple additive contribution. Indeed, its presence caused metabolic modifications during <it>S. cerevisiae </it>fermentation causing variation in the gene expression and enzymatic activity of alcohol deydrogenase and pyruvate decarboxilase.</p>