The role of flour type and feeding schedule on the sourdough microbiome

Sourdough starters are fermentations of various grains by bacteria and yeast and are of worldwide economic and cultural importance. Sourdoughs are often spontaneously inoculated and their resident microbial communities are in part shaped by environmental factors, potentially including flour, water, air, human microbiota, equipment, geography, and temperature. The number of different genera of bacteria and yeast found in sourdoughs is large, however only a handful of species typically dominate an individual sourdough starter. Understanding how and why certain species form a mature climax community in a particular environment is a key question in microbial ecology. To investigate this question, we tested whether different baking flours (all purpose, bread, and whole wheat) and frequency of feeding, also known as backslopping, shape the sourdough starter microbial community over the course of one month. We found that the yeast genus Kazachstania rapidly rose in frequency and became the dominant yeast in all starters, regardless of flour type or feeding schedule. In contrast, flour type did affect the bacterial community. Mature sourdoughs all contained the bacterial genera Companilactobacillus, Levilactobacillus, Lactiplantibacillus, Furfurilactobacillus, and Acetobacter, with Companilactobacillus dominant in whole wheat flour, and Levilactobacillus more prevalent in bread flour. We identified a significant effect of starter flour type on the leavening rate of bread dough. We conclude that flour can shape the microbial community of sourdough and has potential implications for functional traits.