Genotypic and phenotypic diversity of Lactobacillus rossiae isolated from beer

Aims Over the past few years, the lactic acid bacteria (LAB) species Lactobacillus rossiae has appeared on occasion as a beer spoiler, in addition to its role as an inhabitant of sourdough and other foods. Many authors have described the L. rossiae sourdough isolates as phenotypically and genotypically extremely versatile. This characterization was confirmed in a comprehensive genotypic and phenotypic study based on 11 beer‐related L. rossiae isolates. Materials and methods The beer‐related isolates and the L. rossiae type strain were classified in a polyphasic approach applying 16S rRNA, rpoA and pheS housekeeping gene sequence comparisons, DNA–DNA hybridization and rep‐PCR technique. Additionally, carbohydrate fermentation and amino‐acid metabolism were examined. In terms of the beer‐spoilage ability, the growth in two different beer types was examined and the presence of three prominent hop resistance genes (horA, horC and hitA) and of one gene presumably responsible for the production of exopolysaccharides (gtf) was checked. Conclusion The carbohydrate fermentation pattern (GTG)5 rep‐PCR and the pheS gene sequence comparison showed deviations between sourdough and beer‐related isolates. DNA–DNA hybridization values and the pheS gene sequence comparison between beer‐related isolates point towards the need for expansion of the limits for species description. Significance and Impact of the Study Lactobacillus rossiae shows great phenotypic and genotypic variability stretching the limits of species description. The correlation between pheS gene sequence and the presence of the horC gene is important for brewing microbiologists and the search for beer‐spoilage prediction methods.