Complexity of yeast/bacteria interactions in wheat sourdough microbial communities
Résumé
A single sourdough usually harbors few dominant yeast species and lactic acid bacteria species, making it very appealing for studying processes behind diversity patters, particularly biotic interactions. In sourdough, it is believed that yeasts and LABs interact mainly in a non-competitive way by mutualistic supply of important metabolites (nutrient, vitamins, ...). However, sourdough interspecific interactions have not yet been extensively analyzed.
We have studied the complexity of yeast/bacteria interactions. First, we reviewed publications that documented yeast and bacteria in sourdoughs and test for co-occurrence. Second, we analyzed the nature of yeast/bacteria strains interaction in the laboratory. We compared growth of yeast and bacteria strains when cultivated alone or together in wheat flour filtrate or wheat dough. The analysis of co-occurrence revealed that Kazachstania humilis and Lactobacillus sanfranciscensis co-occurred more often than expected by chance while Wickeranomyces anomalus and L. sanfranciscensis co-occurred less often. We tested whether K. humilis and L. sanfranciscensis were in positive interaction but also studied other yeast/bacteria species that can be found in sourdough. We found that the effect of the yeast-LAB interaction depends on the strains rather than the species. Globally, the response was asymmetric. Yeasts facilitated the growth of bacteria in several cases, but the opposite was not found. The nature of interaction differed in liquid wheat flour filtrate and dough, showing an environment effect. All together our data revealed the complexity of yeast/bacteria interactions.