Comparative Genomics of Lactobacillus brevis Reveals a Significant Plasmidome Overlap of Brewery and Insect Isolates.

Lactobacillus (L.) brevis represents a versatile, ubiquitistic species of lactic acid bacteria, occurring in various foods, as well as plants and intestinal tracts. The ability to deal with considerably differing environmental conditions in the respective ecological niches implies a genomic adaptation to the particular requirements to use it as a habitat beyond a transient state. Given the isolation source, 24 L. brevis genomes were analyzed via comparative genomics to get a broad view of the genomic complexity and ecological versatility of this species. This analysis showed L. brevis being a genetically diverse species possessing a remarkably large pan genome. As anticipated, it proved difficult to draw a correlation between chromosomal settings and isolation source. However, on plasmidome level, brewery- and insect-derived strains grouped into distinct clusters, referable to a noteworthy gene sharing between both groups. The brewery-specific plasmidome is characterized by several genes, which support a life in the harsh environment beer, but 40% of the brewery plasmidome were found in insect-derived strains as well. This suggests a close interaction between these habitats. Further analysis revealed the presence of a truncated horC cluster version in brewery- and insect-associated strains. This disproves horC, the major contributor to survival in beer, as brewery isolate specific. We conclude that L. brevis does not perform rigorous chromosomal changes to live in different habitats. Rather it appears that the species retains a certain genetic diversity in the plasmidome and meets the requirements of a particular ecological niche with the acquisition of appropriate plasmids.

Influence of Different Sugars and Initial pH on ß-Glucan Formation by Lactobacillus brevis TMW 1.2112.

We wanted to identify key factors influencing the extent of ß-glucan production by Lactobacillus brevis TMW 1.2112, which has been isolated from viscous, spoiled beer and which could contribute to viscosity increases of spoiled beverages via exopolysaccharide (EPS) production. In this way, we analyzed the influence of different initial pH values and carbohydrate sources on growth of and slime/ß-glucan formation by this strain. In a screening of 48 carbohydrates, 14 fermentable sugars which enabled growth were identified. These sugars were further investigated regarding their EPS formation-promoting properties. The hexose-based mono- and di-saccharides enabled slime formation, while all pentoses failed to cause any thickening effect. The strongest slime formation was observed upon growth on D-maltose, the weakest on D-fructose. A lower initial pH (4.3) caused significant higher viscosities than an initially higher one (pH 6.2). This effect was independent from the carbohydrate supplied. Although the thickening of nutrient media by L. brevis TMW 1.2112 strongly depended on the initial pH and the available carbon source, all isolated polysaccharides were exclusively composed of glucose moieties and exhibited highly similar elution profiles after separation via asymmetric flow field-flow fractionation independently of the provided carbon source. Our results suggest that the extent of ß-glucan/slime formation by special L. brevis strains isolated from the brewery environment is strongly influenced by the initial pH and the availability of certain EPS formation-promoting sugars with maltose being the most favored carbohydrate for the regulated and directive biosynthesis of capsular ß-glucan.

Characterization of ß-glucan formation by Lactobacillus brevis TMW 1.2112 isolated from slimy spoiled beer.

Despite several hurdles, which hinder bacterial growth in beer, certain bacteria are still able to spoil beer. One type of spoilage is characterized by an increased viscosity and slimy texture caused by exopolysaccharide (EPS) formation of lactic acid bacteria (LAB). In this study, we characterize for the first time EPS production in a beer-spoiling strain (TMW 1.2112) of Lactobacillus brevis, a species commonly involved in beer spoilage. The strain's growth dynamics were assessed and we found an increased viscosity or ropiness in liquid or on solid media, respectively. Capsular polysaccharides (CPS) and released EPS from the cells or supernatant, respectively, were analyzed via NMR spectroscopy and methylation analysis. Both are identical ß-(1→3)-glucans, which are ramified with ß-glucose residues at position O2. Therefore, we assume that this EPS is mainly produced as CPS and partially released into the surrounding medium, causing viscosity of e.g. beer. CPS formation was confirmed via an agglutination test. A plasmid-located glycosyltransferase-2 was found as responsible for excess ß-glucan formation, chromosomal glucanases were proposed for its degradation. The glycosyltransferase-2 gene could also be specifically identified in beer-spoiling, slime-producing Lactobacillus rossiae and Lactobacillus parabuchneri strains, suggesting it as promising marker gene for the early detection of ß-glucan-producing Lactobacilli in breweries.

Multiple Genome Sequences of Exopolysaccharide-Producing, Brewery-Associated Lactobacillus brevis Strains.

Lactobacillus brevis represents one of the most relevant beer-spoiling bacteria. Besides strains causing turbidity and off flavors upon growth and metabolite formation, this species also comprises strains that produce exopolysaccharides (EPSs), which increase the viscosity of beer. Here, we report the complete genome sequences of three EPS-producing, brewery-associated L. brevis strains.