Comparison of the complete genome sequencesof Bifidobacterium animalis subsp. lactis DSM 10140 and Bl-04

Bifidobacteria are important members of the human gut flora, especially in infants. Comparative genomic analysis of two Bifidobacterium animalis subsp. lactis strains revealed evolution by internal deletion of consecutive spacer-repeat units within a novel clustered regularly interspaced short palindromic repeat locus, which represented the largest differential content between the two genomes. Additionally, 47 single nucleotide polymorphisms were identified, consisting primarily of nonsynonymous mutations, indicating positive selection and/or recent divergence. A particular nonsynonymous mutation in a putative glucose transporter was linked to a negative phenotypic effect on the ability of the variant to catabolize glucose, consistent with a modification in the predicted protein transmembrane topology. Comparative genome sequence analysis of three Bifidobacterium species provided a core genome set of 1,117 orthologs complemented by a pan-genome of 2,445 genes. The genome sequences of the intestinal bacterium B. animalis subsp. lactis provide insights into rapid genome evolution and the genetic basis for adaptation to the human gut environment, notably with regard to catabolism of dietary carbohydrates, resistance to bile and acid, and interaction with the intestinal epithelium. The high degree of genome conservation observed between the two strains in terms of size, organization, and sequence is indicative of a genomically monomorphic subspecies and explains the inability to differentiate the strains by standard techniques such as pulsed-field gel electrophoresis

Transport of Glucose by Bifidobacterium animalis subsp. lactis Occurs via Facilitated Diffusion▿

Two strains of Bifidobacterium animalis subsp. lactis were indistinguishable by several nucleic acid-based techniques; however, the type strain DSMZ 10140 was glucose utilization positive, while RB 4825, an industrially employed strain, was unable to grow rapidly on glucose as the principal carbon source. This difference was attributed to the presence of a low-affinity facilitated-diffusion glucose transporter identified in DSMZ 10140 but lacking in RB 4825. Uptake of d-[U-14C]glucose in DSMZ 10140 was stimulated by monovalent cations (ammonium, sodium, potassium, and lithium) and inhibited by divalent cations (calcium and magnesium). When competitor carbohydrates were included in the uptake assays, stereospecific inhibition was exhibited, with greater competition by methyl-β-glucoside than methyl-α-glucoside. Significant inhibition (>30%) was observed with phloretin, an inhibitor of facilitated diffusion of glucose, whereas there was no inhibition by sodium fluoride, iodoacetate, sodium arsenate, sodium azide, 2,4-dinitrophenol, monensin, or valinomycin, which typically reduce energy-driven transport. Based on kinetic analyses, the mean values for Kt and Vmax were 14.8 ± 3.4 mM d-glucose and 0.13 ± 0.03 μmol glucose/min/mg cell protein, respectively. Glucose uptake by several glucose-utilizing commercial strains of B. animalis subsp. lactis was also inhibited by phloretin, indicating the presence of facilitated diffusion glucose transporters in those strains. Since DSMZ 10140 has been previously reported to lack a functional glucose phosphoenolpyruvate phosphotransferase system, the glucose transporter identified here is responsible for much of the organism's glucose uptake

Intrinsic and inducible resistance to hydrogen peroxide in \u3ci\u3eBifidobacterium\u3c/i\u3e species

Interest in, and use of, bifidobacteria as a probiotic delivered in functional foods has increased dramatically in recent years. As a result of their anaerobic nature, oxidative stress can pose a major challenge to maintaining viability of bifidobacteria during functional food storage. To better understand the oxidative stress response in two industrially important bifidobacteria species, we examined the response of three strains of B. longum and three strains of B. animalis subsp. lactis to hydrogen peroxide (H2O2). Each strain was exposed to a range of H2O2 concentrations (0–10 mM) to evaluate and compare intrinsic resistance to H2O2. Next, strains were tested for the presence of an inducible oxidative stress response by exposure to a sublethal H2O2 concentration for 20 or 60 min followed by challenge at a lethal H2O2 concentration. Results showed B. longum subsp. infantis ATCC 15697 had the highest level of intrinsic H2O2 resistance of all strains tested and B. animalis subsp. lactis BL-04 had the highest resistance among B. lactis strains. Inducible H2O2 resistance was detected in four strains, B. longum NCC2705, B. longum D2957, B. lactis RH-1, and B. lactis BL-04. Other strains showed either no difference or increased sensitivity to H2O2 after induction treatments. These data indicate that intrinsic and inducible resistance to hydrogen peroxide is strain specific in B. longum and B. lactis and suggest that for some strains, sublethal H2O2 treatments might help increase cell resistance to oxidative damage during production and storage of probiotic-containing foods