Polyphasic taxonomic characterization of Lactobacillus rossiae isolates from Belgian and Italian sourdoughs reveals intraspecific heterogeneity

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.

Microbial Ecology and Process Technology of Sourdough Fermentation

From a microbiological perspective, sourdough is to be considered as a specific and stressful ecosystem, harboring yeasts and lactic acid bacteria (LAB), that is used for the production of baked goods. With respect to the metabolic impact of the sourdough microbiota, acidification (LAB), flavor formation (LAB and yeasts), and leavening (yeasts and heterofermentative LAB species) are most noticeable. Three distinct types of sourdough fermentation processes can be discerned based on the inocula applied, namely backslopped ones (type 1), those initiated with starter cultures (type 2), and those initiated with a starter culture followed by backslopping (type 3). A sourdough-characteristic LAB species is Lactobacillus sanfranciscensis. A sourdough-characteristic yeast species is Candida humilis. Although it has been suggested that the microbiota of a specific sourdough may be influenced by its geographical origin, region specificity often seems to be an artefact resulting from interpretation of the research data, as those are dependent on sampling, isolation, and identification procedures. It is however clear that sourdough-adapted microorganisms are able to withstand stress conditions encountered during their growth. Based on the technological setup, type 0 (predoughs), type I (artisan bakery firm sourdoughs), type II (industrial liquid sourdoughs), and type III sourdoughs (industrial dried sourdoughs) can be distinguished. The production of all sourdoughs, independent of their classification, depends on several intrinsic and extrinsic factors. Both the flour (type, quality status, etc.) and the process parameters (fermentation temperature, pH and pH evolution, dough yield, water activity, oxygen tension, backslopping procedure and fermentation duration, etc.) determine the dynamics and outcome of (backslopped) sourdough fermentation processes.

Cloning, expression and characterization of a β-D-xylosidase from Lactobacillus rossiae DSM 15814(T)

BACKGROUND

Among the oligosaccharides that may positively affect the gut microbiota, xylo-oligosaccharides (XOS) and arabinoxylan oligosaccharides (AXOS) possess promising functional properties. Ingestion of XOS has been reported to contribute to anti-oxidant, anti-bacterial, immune-modulatory and anti-diabetic activities. Because of the structural complexity and chemical heterogeneity, complete degradation of xylan-containing plant polymers requires the synergistic activity of several enzymes. Endo-xylanases and β-D-xylosidases, collectively termed xylanases, represent the two key enzymes responsible for the sequential hydrolysis of xylan. Xylanase cocktails are used on an industrial scale for biotechnological purposes. Lactobacillus rossiae DSM 15814(T) can utilize an extensive set of carbon sources, an ability that is likely to contribute to its adaptive ability. In this study, the capacity of this strain to utilize XOS, xylan, D-xylose and L-arabinose was investigated.

RESULTS

Genomic and transcriptomic analyses revealed the presence of two gene clusters, designated xyl and ara, encoding proteins predicted to be responsible for XOS uptake and hydrolysis and D-xylose utilization, and L-arabinose metabolism, respectively. The deduced amino acid sequence of one of the genes of the xyl gene cluster, LROS_1108 (designated here as xylA), shows high similarity to (predicted) β-D-xylosidases encoded by various lactic acid bacteria, and belongs to glycosyl hydrolase family 43. Heterologously expressed XylA was shown to completely hydrolyse XOS to xylose and showed optimal activity at pH 6.0 and 40 °C. Furthermore, β-D-xylosidase activity of L. rossiae DSM 15814(T) was also measured under sourdough conditions.

CONCLUSIONS

This study highlights the ability of L. rossiae DSM 15814(T) to utilize XOS, which is a very useful trait when selecting starters with specific metabolic performances for sourdough fermentation or as probiotics.

Lactobacillus rossiae, a vitamin B12 producer, represents a metabolically versatile species within the Genus Lactobacillus

Lactobacillus rossiae is an obligately hetero-fermentative lactic acid bacterium, which can be isolated from a broad range of environments including sourdoughs, vegetables, fermented meat and flour, as well as the gastrointestinal tract of both humans and animals. In order to unravel distinctive genomic features of this particular species and investigate the phylogenetic positioning within the genus Lactobacillus, comparative genomics and phylogenomic approaches, followed by functional analyses were performed on L. rossiae DSM 15814^T, showing how this type strain not only occupies an independent phylogenetic branch, but also possesses genomic features underscoring its biotechnological potential. This strain in fact represents one of a small number of bacteria known to encode a complete de novo biosynthetic pathway of vitamin B₁₂ (in addition to other B vitamins such as folate and riboflavin). In addition, it possesses the capacity to utilize an extensive set of carbon sources, a characteristic that may contribute to environmental adaptation, perhaps enabling the strain's ability to populate different niches.

Microbial ecology of sourdough fermentations: diverse or uniform?

Sourdough is a specific and stressful ecosystem inhabited by yeasts and lactic acid bacteria (LAB), mainly heterofermentative lactobacilli. On the basis of their inocula, three types of sourdough fermentation processes can be distinguished, namely backslopped ones, those initiated with starter cultures, and those initiated with a starter culture followed by backslopping. Typical sourdough LAB species are Lactobacillus fermentum, Lactobacillus paralimentarius, Lactobacillus plantarum, and Lactobacillus sanfranciscensis. Typical sourdough yeast species are Candida humilis, Kazachstania exigua, and Saccharomyces cerevisiae. Whereas region specificity is claimed in the case of artisan backslopped sourdoughs, no clear-cut relationship between a typical sourdough and its associated microbiota can be found, as this is dependent on the sampling, isolation, and identification procedures. Both simple and very complex consortia may occur. Moreover, a series of intrinsic and extrinsic factors may influence the composition of the sourdough microbiota. For instance, an influence of the flour (type, quality status, etc.) and the process parameters (temperature, pH, dough yield, backslopping practices, etc.) occurs. In this way, the presence of Lb. sanfranciscensis during sourdough fermentation depends on specific environmental and technological factors. Also, Triticum durum seems to select for obligately heterofermentative LAB species. Finally, there are indications that the sourdough LAB are of intestinal origin.

Draft genome sequence of Lactobacillus rossiae DSM 15814(T)

The draft genome sequence of Lactobacillus rossiae DSM 15814(T) (CS1, ATCC BAA-88) was determined by a whole-genome shotgun approach. Reads were assembled to a 2.9-Mb draft version. RAST genome annotation evidenced 2,723 predicted coding sequences. Many carbohydrate, amino acid, and amino acid derivative subsystem features were found.