Does strain-level persistence of lactobacilli in long-term back-slopped sourdoughs inform on domestication of food-fermenting lactic acid bacteria?

ABSTRACT Sourdoughs are maintained by back-slopping over long time periods. To determine strain-level persistence of bacteria, we characterized four sourdoughs from bakeries over a period of 3.3, 11.0, 18.0, and 19.0 years. One sourdough included isolates of Levilactobacillus spp. and Fructilactobacillus spp. that differed by fewer than 10 single-nucleotide polymorphisms (SNPs) from the isolates obtained 3.3 years earlier and thus likely represent the same strain. Isolates of Levilactobacillus parabrevis differed by 200–300 SNPs; their genomes were under positive selection, indicating transmission from an external source. In two other sourdoughs, isolates of Fructilactobacillus sanfranciscensis that were obtained 11 and 18 years apart differed by 19 and 29 SNPs, respectively, again indicating repeated isolation of the same strain. The isolate of Fl. sanfranciscensis from the fourth sourdough differed by 45 SNPs from the isolate obtained 19 years previously. We thus identified strain-level persistence in three out of four long-term back-slopped sourdoughs, making it possible that strains persisted over periods that are long enough to allow bacterial speciation and domestication. IMPORTANCE The assembly of microbial communities in sourdough is shaped by dispersal and selection. Speciation and domestication of fermentation microbes in back-slopped food fermentations have been documented for food-fermenting fungi including sourdough yeasts but not for bacteria, which evolve at a slower rate. Bacterial speciation in food fermentations requires strain-level persistence of fermentation microbes over hundreds or thousands of years. By documenting strain-level persistence in three out of four sourdoughs over a period of up to 18 years, we demonstrate that persistence over hundreds or thousands of years is possible, if not likely. We thus not only open a new perspective on fermentation control in bakeries but also support the possibility that all humans, despite their cultural diversity, share the same fermentation microbes.