Genomic and physiological insights into the lifestyle of Bifidobacterium species from water kefir.

Water kefir is a fermented beverage employing a natural microbial consortium, which harbours bifidobacteria, namely Bifidobacterium aquikefiri and Bifidobacterium tibiigranuli. However, little information is available on their metabolic properties or role in the consortium. In this study, we combined genomic and physiologic investigations to predict and characterize the properties of these organisms and their possible role in the consortium. When comparing the genomes of these psychrotrophic organisms with that of the three selected mesophilic probiotic Bifidobacterium strains, we could find 143 genes shared by the 3 known isolates of bifidobacteria from water kefir that do not occur in the probiotic strains. These include genes involved in acid and oxygen tolerance. In addition, their genomically predicted carbohydrate usage and transport suggest adaptation to sucrose and other plant-related sugars. Furthermore, they proved prototrophic for all amino acids in vitro, which enables them to cope with the strong amino acid limitation in water kefir.

Bifidobacterium tibiigranuli sp. nov. isolated from homemade water kefir.

Two Bifidobacterium strains, TMW 2.2057T and TMW 2.1764 were isolated from two different homemade water kefirs from Germany. Both strains were oxidase- and catalase-negative and Gram-staining-positive. Cells were non-motile, irregular rods that were aerotolerant anaerobes. On basis of fructose 6-phosphate phosphoketolase activity, they were assigned to the family Bifidobacteriaceae. Comparative analysis of 16S rRNA and concatenated housekeeping genes (clpC, dnaB, dnaG, dnaJ, hsp60 and rpoB) demonstrated that both strains represented a member of the genus Bifidobacterium, with Bifidobacterium subtile DSM 20096T as the closest phylogenetic relative (98.35 % identity). Both strains can be distinguished using randomly amplified polymorphic DNA fingerprinting. Analysis of concatenated marker gene sequences as well as average nucleotide identity by blast (ANIb) and in silico DNA-DNA hybridization (isDDH) calculations of their genome sequences confirmed Bifidobacterium subtile DSM 20096T as the closest relative (87.91 and 35.80 % respectively). All phylogenetic analyses allow differentiation of strains TMW 2.2057T and TMW 2.1764 from all hitherto described species of the genus Bifidobacterium with validly published names. We therefore propose a novel species with the name Bifidobacterium tibiigranuli, for which TMW 2.2057T (=DSM 108414T=LMG 31086T) is the type strain.

In situ production and characterization of cloud forming dextrans in fruit-juices.

Turbidity in beverages is typically achieved by addition of emulsion based cloud systems. Their intrinsic instability necessitates the widespread use of technological measures and use of food additives to prevent emulsion decay. In this work, we explored the possibility to establish a new generation of natural, stable clouding systems based on bacterial dextrans. Lactobacillus hordei TMW 1.1907 originating from water kefir was used to produce dextrans in sucrose supplemented apple or grape juices. By varying the fermentation conditions, two distinct types of dextran molecules could be produced at yields ranging from 2.5 to 8.5 g/L. The dextran-containing fermentates showed an unchanged turbidity after pasteurization at acidic pH and subsequent storage for three months. No sedimentation of particles occurred upon storage. Neutralization of the acidic fruit juices to pH 7 prior to fermentation significantly increased the dextran yields. The molecular weight, rms radii and turbidity of dextrans produced at 20 °C were higher than those produced at 30 °C. Characterization of the isolated dextrans by asymmetric flow field-flow fractionation coupled to multi-angle laser light scattering revealed a random-coil like structure and rms radii ranging from 66.0 to 87.4 nm. The averaged molar masses of the cloud forming dextrans were in the approximate range of 103.1 to 141.6 MDa. In conclusion, our results demonstrate the possibility to ferment fruit juices for in situ production of dextrans exhibiting novel techno-functional properties beyond gelling and thickening.