Mutually stimulating interactions between lactic acid bacteria and Saccharomyces cerevisiae in sourdough fermentation

Interactions between microorganisms are key to their performance in food habitats. Improved understanding of these interactions supports rational improvement of food fermentations. This study aimed at identifying interactions between lactic acid bacteria and yeast during sourdough fermentation. Therefore, the lactic acid bacteria Lactobacillus plantarum and Lactobacillus sanfranciscensis were co-cultured with the yeast Saccharomyces cerevisiae in a newly developed medium, as well as in situ in a sourdough-like environment. L. sanfranciscensis was found to be stimulated by a secreted factor of S. cerevisiae in any tested in vitro situation, whereas L. plantarum and S. cerevisiae stimulated each other only in the presence of glucose, fructose and lactose as carbon source, but not with galactose, maltose, sucrose and starch. Moreover, it was demonstrated that L. sanfranciscensis is stimulated by CO2 and another yet to be identified factor produced by yeast in a sourdough-like environment. In conclusion, S. cerevisiae produces growth factors stimulatory to lactic bacteria. The nature and the efficacy of these growth factors depend on the target species and on the supplied carbon source.