Strain-specific interaction of Fructilactobacillus sanfranciscensis with yeasts in the sourdough fermentation

Fructilactobacillus (F.) sanfranciscensis is a key bacterium in traditional (type 1) sourdough fermentations. It typically occurs in combination with the sourdough yeast Kazachstania (K.) humilis or the generalist Saccharomyces (S.) cerevisiae . Previous studies revealed intra-species diversity in competitiveness or dominance in sourdoughs of F. sanfranciscensis , as well as preferences for a life with or without a specific yeast. In this study representative, differently behaving strains were studied in media with different sugars and electron acceptors, and in rye sourdough fermentations in the presence and absence of K. humilis or S. cerevisiae . Strain-specific differences were observed in sugar and organic acids spectra in media, and in sourdoughs with F. sanfranciscensis strains in combination with K. humilis or S. cerevisiae . F. sanfranciscensis TMW 1.1150 proved dominant in the presence and absence of any yeast because it most effectively used maltose. Its maltose fermentation was unaffected by electron acceptors. F. sanfranciscensis TMW 1.2138 was the weakest maltose fermenter and incapable of glucose fermentation, and evidently not competitive against the other strains. F. sanfranciscensis TMW 1.392 was the most versatile strain regarding the utilization of different carbohydrates and its ability to exploit electron acceptors like fructose and oxygen. In sourdoughs without yeasts, it outcompeted other strains. The metabolism of F. sanfranciscensis TMW 1.907 was stimulated in combination with S. cerevisiae . In competitive trials, it was assertive only with S. cerevisiae . The intra-species differences in carbohydrate metabolism can widely explain the differences in their behavior in sourdough fermentation. Interaction between F. sanfranciscensis and the yeasts was strain specific and supposedly commensal with K. humilis and rather competitive with S. cerevisiae .