Role ofKazachstania humilisandSaccharomyces cerevisiaein the strain-specific assertiveness ofFructilactobacillus sanfranciscensisstrains in rye sourdough

Sourdough is a common ingredient for baked goods as it improves their texture, shelf life and flavor. One of the dominant key species in type I sourdoughs isFructilactobacillus sanfranciscensis(formerlyLactobacillus sanfranciscensis), which occurs with a multitude of different strains. Noticeably, this species often shares its habitat with the yeastsSaccharomyces cerevisiaeorKazachstania humilis. It is still unclear, which relationship exists between these organisms and whether it is characterized by coexistence, interaction, or mutualism. In this study, competitiveness of differentF. sanfranciscensisstrains in rye sourdough was examined and its dependence of co-existing yeasts was explored. In particular, it was investigated whether competitiveness ofF. sanfranciscensisstrains depends on the presence/absence ofS. cerevisiaeorK. humiliswhen co-inoculated in the sourdough. Competitiveness of strains was monitored in rye sourdough using the CRISPR locus length polymorphism (CLLP)-PCR for strain differentiation. It was found thatF. sanfranciscensisTMW 1.1150, TMW 1.1221 and TMW 1.1597 were dominant regardless of the presence/absence of both yeast species. Dominance ofF. sanfranciscensisTMW 1.392, TMW 1.907 and TMW 1.2137 was significantly and diversely influenced by the presence ofS. cerevisiaeorK. humilis.F. sanfranciscensisTMW 1.2138 and TMW 1.726 were not able to compete against the otherF. sanfranciscensisstrains. It was possible to sort the eight strains into three different groups: 1. Strain competitiveness was independent of the presence/absence of yeasts; 2. Strain competitiveness was dependent on yeast species and 3. Strains were not competitive in the presence of strains belonging to group 1 or 2. Interestingly, in fermentations that were not inoculated with any yeast a spontaneous occurrence ofS. cerevisiaeorK. humiliswas observed depending on the synergistic competitiveness of the respectiveF. sanfranciscensisused. Thus, the level of competitiveness was strain specific and, in some strains, dependent on the presence/absence of specific yeast species.