Comparative Genomics of Bifidobacterium animalis subsp. lactis Reveals a Strict Monophyletic Bifidobacterial Taxon

Strains of Bifidobacterium animalis subsp. lactis are extensively exploited by the food industry as health-promoting bacteria, although the genetic variability of members belonging to this taxon has so far not received much scientific attention. In this article, we describe the complete genetic makeup of the B. animalis subsp. lactis Bl12 genome and discuss the genetic relatedness of this strain with other sequenced strains belonging to this taxon. Moreover, a detailed comparative genomic analysis of B. animalis subsp. lactis genomes was performed, which revealed a closely related and isogenic nature of all currently available B. animalis subsp. lactis strains, thus strongly suggesting a closed pan-genome structure of this bacterial group.     

Genome Sequence of the Probiotic Bacterium Bifidobacterium animalis subsp. lactis AD011

Bifidobacterium animalis subsp. lactis is a probiotic bacterium that naturally inhabits the guts of most mammals, including humans. Here we report the complete genome sequence of B. animalis subsp. lactis AD011 that was isolated from an infant fecal sample. Biological functions encoded in a single circular chromosome of 1,933,695 bp, smallest among the completely sequenced bifidobacterial genomes, are suggestive of their probiotic functions, such as utilization of bifidogenic factors and a variety of glycosidic enzymes and biosynthesis of polysaccharides.     

Comparative Sequence Analysis of the tuf and recA Genes and Restriction Fragment Length Polymorphism of the Internal Transcribed Spacer Region Sequences Supply Additional Tools for Discriminating Bifidobacterium lactis from Bifidobacterium animalis

The relationship between Bifidobacterium lactis and Bifidobacterium animalis was examined by comparative analysis of tuf and recA gene sequences and by restriction fragment length polymorphism analysis of their internal 16S-23S transcribed spacer region sequences. The bifidobacterial strains investigated could be divided into two distinct groups within a single species based on the tuf, recA, and 16S-23S spacer region sequence analysis. Therefore, all strains of B. lactis and B. animalis could be unified as the species B. animalis and divided into two subspecies, Bifidobacterium animalis subsp. lactis and Bifidobacterium animalis subsp. animalis.     

Complete Genome Sequence of Probiotic Bifidobacterium animalis subsp. lactis Strain V9

Bifidobacterium animalis subsp. lactis strain V9 is a Chinese commercial bifidobacteria with several probiotic functions. It was isolated from a healthy Mongolian child in China. We present here the complete genome sequence of V9 and compare it to 3 other published genome sequences of B. animalis subsp. lactis strains. The result indicates the lack of polymorphism among strains of this subspecies from different continents.Bifidobacterium animalis subsp. lactis strain V9 was isolated from the feces of a healthy Mongolian child in China (5). It has shown a high level of tolerance to gastric acid and bile acids (5). This strain has been implemented in the industrial production of dairy starter cultures by Inner Mongolia Yili Industrial Group Company Limited, the largest dairy corporation in China.Whole-genome sequencing of B. animalis subsp. lactis V9 was performed with a combined strategy of 454 sequencing (8) and Solexa paired-end sequencing technology (2). Genomic libraries containing 7-kb inserts were constructed, and 325,824 paired-end reads and 67,177 single-end reads were generated using the GS FLX system, giving 36.0-fold coverage of the genome. A total of 96.0% of the reads were assembled into four large scaffolds, including 163 nonredundant contigs, using the 454 Newbler assembler (454 Life Sciences, Branford, CT). A total of 8,953,102 reads (2-kb library) were generated to reach a depth of 335-fold coverage with an Illumina Solexa Genome Analyzer IIx and mapped to the scaffolds using the Burrows-Wheeler Alignment (BWA) tool (7). The gaps between scaffolds were filled by sequencing PCR products using an ABI 3730 capillary sequencer. The analysis of the genome was performed as described previously (3, 4).The complete genome sequence of V9 contains a circular 1,944,050-bp chromosome, with a GC content of 60.5%. The genome size is slightly larger than the sequenced genome sizes of B. animalis subsp. lactis strains DSM 10140^T (1), Bl-04 (1), and AD011 (6) due to a unique insertion of 4,037 bp. The V9 genome contains 1,636 genes in total, including 1,572 coding genes, 4 rRNA operons, and 52 tRNAs.Comparison of the four B. animalis subsp. lactis genomes revealed nearly perfect synteny. AD011 is the most diverged strain, with more single nucleotide polymorphisms (SNPs) and indels than the other three strains. There are 197 SNPs in AD011, with 70 synonymous and 16 nonsynonymous SNPs, which means that there is only 1 SNP per 10 kb, indicating the high consistency within this subspecies. The other three strains are almost identical, with only 25 SNPs in V9, 13 SNPs in Bl-04, and 44 SNPs in DSM 10140^T. Strain V9 was isolated from the feces of a Mongolian child in Inner Mongolia, China, where traditional fermented milk has been consumed for thousands of years, and the other three strains were originally isolated from fecal samples (1, 6) or yogurt (1) in the United States of America, France, and Korea. The result indicated the lack of polymorphism among multiple lineages from different continents (1).Interestingly, compared to the other three sequenced B. animalis subsp. lactis strains, V9 has a large insertion, which encodes one putative transposase (BalV_1091) and two sugar metabolism-related proteins, an alpha-1,4-glucosidase (BalV_1092) and an ABC transporter solute-binding protein (BalV_1093). This insertion is a copy of the region at positions 1,860,164 to 1,864,073, which is commonly shared by all four B. animalis subsp. lactis strains.     

Identification of Restriction-Modification Systems of Bifidobacterium animalis subsp. lactis CNCM I-2494 by SMRT Sequencing and Associated Methylome Analysis

Bifidobacterium animalis subsp. lactis CNCM I-2494 is a component of a commercialized fermented dairy product for which beneficial effects on health has been studied by clinical and preclinical trials. To date little is known about the molecular mechanisms that could explain the beneficial effects that bifidobacteria impart to the host. Restriction-modification (R-M) systems have been identified as key obstacles in the genetic accessibility of bifidobacteria, and circumventing these is a prerequisite to attaining a fundamental understanding of bifidobacterial attributes, including the genes that are responsible for health-promoting properties of this clinically and industrially important group of bacteria. The complete genome sequence of B. animalis subsp. lactis CNCM I-2494 is predicted to harbour the genetic determinants for two type II R-M systems, designated BanLI and BanLII. In order to investigate the functionality and specificity of these two putative R-M systems in B. animalis subsp. lactis CNCM I-2494, we employed PacBio SMRT sequencing with associated methylome analysis. In addition, the contribution of the identified R-M systems to the genetic accessibility of this strain was assessed.     

Genomic Insights into Bifidobacteria

Summary: Since the discovery in 1899 of bifidobacteria as numerically dominant microbes in the feces of breast-fed infants, there have been numerous studies addressing their role in modulating gut microflora as well as their other potential health benefits. Because of this, they are frequently incorporated into foods as probiotic cultures. An understanding of their full interactions with intestinal microbes and the host is needed to scientifically validate any health benefits they may afford. Recently, the genome sequences of nine strains representing four species of Bifidobacterium became available. A comparative genome analysis of these genomes reveals a likely efficient capacity to adapt to their habitats, with B. longum subsp. infantis exhibiting more genomic potential to utilize human milk oligosaccharides, consistent with its habitat in the infant gut. Conversely, B. longum subsp. longum exhibits a higher genomic potential for utilization of plant-derived complex carbohydrates and polyols, consistent with its habitat in an adult gut. An intriguing observation is the loss of much of this genome potential when strains are adapted to pure culture environments, as highlighted by the genomes of B. animalis subsp. lactis strains, which exhibit the least potential for a gut habitat and are believed to have evolved from the B. animalis species during adaptation to dairy fermentation environments.     

母乳源乳双歧杆菌Probio-M8的遗传特征及基因组差异比较分析

【目的】母乳源乳双歧杆菌（Bifidobacterium animalis subsp. lactis） Probio-M8具有优良的益生特性,本文拟从全基因组水平解析Probio-M8的遗传特征,并与已有益生功效的乳双歧杆菌的基因组进行比较分析。【方法】本研究基于NCBI已公开的21株乳双歧杆菌和1株模式菌株DSM10140^T的基因组数据,构建了核心基因集与泛基因集,解析该群体的系统发育关系,比较分析Probio-M8的遗传特征及功能基因组。【结果】22株乳双歧杆菌的泛基因集包含1 618个基因,其中核心基因1 514个,占泛基因集的93.57%,表明乳双歧杆菌核心基因集高度保守。以1 514个核心基因构建系统发育树,发现22株乳双歧杆菌分为两个分支,AD011单独为一个分支,Probio-M8和其他菌株与模式菌株DSM10140^T聚在同一分支,且Probio-M8与V9、BB-12、Bi-07、HN019的遗传距离极为接近。进一步分析耐药基因和毒力基因,在Probio-M8与V9、BB-12、Bi-07、HN019基因组上均检测到DfrA...     

Enzymatic Ability of Bifidobacterium animalis subsp. lactis To Hydrolyze Milk Proteins: Identification and Characterization of Endopeptidase O

The proteolytic system of Bifidobacterium animalis subsp. lactis was analyzed, and an intracellular endopeptidase (PepO) was identified and characterized. This work reports the first complete cloning, purification, and characterization of a proteolytic enzyme in Bifidobacterium spp. Aminopeptidase activities (general aminopeptidases, proline iminopeptidase, X-prolyl dipeptidylaminopeptidase) found in cell extracts of B. animalis subsp. lactis were higher for cells that had been grown in a milk-based medium than for those grown in MRS. A high specific proline iminopeptidase activity was observed in B. animalis subsp. lactis. Whole cells and cell wall-bound protein fractions showed no caseinolytic activity; however, the combined action of intracellular proteolytic enzymes could hydrolyze casein fractions rapidly. The endopeptidase activity of B. animalis subsp. lactis was examined in more detail, and the gene encoding an endopeptidase O in B. animalis subsp. lactis was cloned and overexpressed in Escherichia coli. The deduced amino acid sequence for B. animalis subsp. lactis PepO indicated that it is a member of the M13 peptidase family of zinc metallopeptidases and displays 67.4% sequence homology with the predicted PepO protein from Bifidobacterium longum. The recombinant enzyme was shown to be a 74-kDa monomer. Activity of B. animalis subsp. lactis PepO was found with oligopeptide substrates of at least 5 amino acid residues, such as met-enkephalin, and with larger substrates, such as the 23-amino-acid peptide α_s1-casein(f1-23). The predominant peptide bond cleaved by B. animalis subsp. lactis PepO was on the N-terminal side of phenylalanine residues. The enzyme also showed a post-proline secondary cleavage site.     

Genes but not genomes reveal bacterial domestication of Lactococcus lactis

Background

The population structure and diversity of Lactococcus lactis subsp. lactis, a major industrial bacterium involved in milk fermentation, was determined at both gene and genome level. Seventy-six lactococcal isolates of various origins were studied by different genotyping methods and thirty-six strains displaying unique macrorestriction fingerprints were analyzed by a new multilocus sequence typing (MLST) scheme. This gene-based analysis was compared to genomic characteristics determined by pulsed-field gel electrophoresis (PFGE).

Methodology/Principal Findings

The MLST analysis revealed that L. lactis subsp. lactis is essentially clonal with infrequent intra- and intergenic recombination; also, despite its taxonomical classification as a subspecies, it displays a genetic diversity as substantial as that within several other bacterial species. Genome-based analysis revealed a genome size variability of 20%, a value typical of bacteria inhabiting different ecological niches, and that suggests a large pan-genome for this subspecies. However, the genomic characteristics (macrorestriction pattern, genome or chromosome size, plasmid content) did not correlate to the MLST-based phylogeny, with strains from the same sequence type (ST) differing by up to 230 kb in genome size.

Conclusion/Significance

The gene-based phylogeny was not fully consistent with the traditional classification into dairy and non-dairy strains but supported a new classification based on ecological separation between “environmental” strains, the main contributors to the genetic diversity within the subspecies, and “domesticated” strains, subject to recent genetic bottlenecks. Comparison between gene- and genome-based analyses revealed little relationship between core and dispensable genome phylogenies, indicating that clonal diversification and phenotypic variability of the “domesticated” strains essentially arose through substantial genomic flux within the dispensable genome.     

Adaptation and Response of Bifidobacterium animalis subsp. lactis to Bile: a Proteomic and Physiological Approach

Bile salts are natural detergents that facilitate the digestion and absorption of the hydrophobic components of the diet. However, their amphiphilic nature makes them very inhibitory for bacteria and strongly influences bacterial survival in the gastrointestinal tract. Adaptation to and tolerance of bile stress is therefore crucial for the persistence of bacteria in the human colonic niche. Bifidobacterium animalis subsp. lactis, a probiotic bacterium with documented health benefits, is applied largely in fermented dairy products. In this study, the effect of bile salts on proteomes of B. animalis subsp. lactis IPLA 4549 and its bile-resistant derivative B. animalis subsp. lactis 4549dOx was analyzed, leading to the identification of proteins which may represent the targets of bile salt response and adaptation in B. animalis subsp. lactis. The comparison of the wild-type and the bile-resistant strain responses allowed us to hypothesize about the resistance mechanisms acquired by the derivative resistant strain and about the bile salt response in B. animalis subsp. lactis. In addition, significant differences in the levels of metabolic end products of the bifid shunt and in the redox status of the cells were also detected, which correlate with some differences observed between the proteomes. These results indicate that adaptation and response to bile in B. animalis subsp. lactis involve several physiological mechanisms that are jointly dedicated to reduce the deleterious impact of bile on the cell's physiology.     

Comparison of the Complete Genome Sequences of 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.Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes are dominant microbial phyla widely distributed in diverse ecosystems on the planet (10, 13, 20, 23, 33, 40, 51). Metagenomic analyses of the microbial landscape inhabiting various mammalian environments, notably the human gastrointestinal tract (GIT) and skin, have specifically identified Actinobacteria as an important and occasionally dominant phylum (18, 21, 33). Among the members of the large, diverse, and dynamic microbial community residing in the human GIT, Bifidobacterium is a dominant genus considered beneficial to humans and includes probiotic strains (live microorganisms which, when administered in adequate amounts, confer a health benefit on the host) (11). The population of bifidobacteria in the human intestine varies over time. Following vaginal delivery, the GIT of healthy newborns is typically colonized by bifidobacteria, especially in breast-fed infants, during the first few days of life (12). Interindividual variation, however, is remarkable in the human infant intestinal flora (41), and dominant genera are not always consistent across metagenomic analyses of the human gut flora (18, 30, 33, 41). Over time, the infant intestinal ecosystem becomes more complex as the diet becomes more diverse, with bifidobacteria typically remaining dominant until weaning (30).Bifidobacterium animalis subsp. lactis is a gram-positive lactic acid bacterium commonly found in the guts of healthy humans and has been identified in the infant gut biota, particularly in ileal, fecal, and mucosal samples (52, 56). Some strains of B. animalis subsp. lactis are able to survive in the GIT, to adhere to human epithelial cells in vitro, to modify fecal flora, to modulate the host immune response, or to prevent microbial gastroenteritis and colitis (4, 15, 20, 40, 52, 56). Additionally, B. animalis subsp. lactis has been reported to utilize nondigestible oligosaccharides, which may contribute to the organism''s ability to compete in the human gut. Carbohydrates resistant to enzymatic degradation and not absorbed in the upper intestinal tract are a primary source of energy for microbes residing in the large intestine. The benefits associated with probiotic strains of B. animalis subsp. lactis have resulted in their inclusion in the human diet via formulation into a large array of dietary supplements and foods, including dairy products such as yogurt. Deciphering the complete genome sequences of such microbes will provide additional insight into the genetic basis for survival and residence in the human gut, notably with regard to the ability to survive gastric passage and utilize available nutrients. Also, these genomes provide reference sequences for ongoing metagenomic analyses of the human environment, including the gut metagenome.Bifidobacterium animalis subsp. lactis is the most common bifidobacterium utilized as a probiotic in commercial dairy products in North America and Europe (22, 38). However, despite this commercial and probiotic significance, strain-level differentiation of B. animalis subsp. lactis strains has been hindered by the high genetic similarity of these organisms, as determined by pulsed-field gel electrophoresis and other nucleic acid-based techniques (6, 55, 56), and the lack of available genomic sequence information. The genome sequence of strain BB-12 (17) is not currently publicly available, and only a draft genome sequence in 28 contigs is available for strain HN019 (GenBank project 28807). The complete B. animalis subsp. lactis genome for strain AD011 (28) was only recently (2009) published. While this was an important first step, a single genome does not allow identification of unique targets for strain differentiation or comparative analyses within the subspecies.The objectives of this study were to determine the complete genome sequences of two B. animalis subsp. lactis strains, the type strain and a widely used commercial strain, to provide insights into the functionality of this species and into species identification and strain specialization.     

Genomic Adaptation of the Lactobacillus casei Group

Lactobacillus casei, L. paracasei, and L. rhamnosus form a closely related taxonomic group (Lactobacillus casei group) within the facultatively heterofermentative lactobacilli. Here, we report the complete genome sequences of L. paracasei JCM 8130 and L. casei ATCC 393, and the draft genome sequence of L. paracasei COM0101, all of which were isolated from daily products. Furthermore, we re-annotated the genome of L. rhamnosus ATCC 53103 (also known as L. rhamnosus GG), which we have previously reported. We confirmed that ATCC 393 is distinct from other strains previously described as L. paracasei. The core genome of 10 completely sequenced strains of the L. casei group comprised 1,682 protein-coding genes. Although extensive genome-wide synteny was found among the L. casei group, the genomes of ATCC 53103, JCM 8130, and ATCC 393 contained genomic islands compared with L. paracasei ATCC 334. Several genomic islands, including carbohydrate utilization gene clusters, were found at the same loci in the chromosomes of the L. casei group. The spaCBA pilus gene cluster, which was first identified in GG, was also found in other strains of the L. casei group, but several L. paracasei strains including COM0101 contained truncated spaC gene. ATCC 53103 encoded a higher number of proteins involved in carbohydrate utilization compared with intestinal lactobacilli, and extracellular adhesion proteins, several of which are absent in other strains of the L. casei group. In addition to previously fully sequenced L. rhamnosus and L. paracasei strains, the complete genome sequences of L. casei will provide valuable insights into the evolution of the L. casei group.     

An Ecological Study of Lactococci Isolated from Raw Milk in the Camembert Cheese Registered Designation of Origin Area

The genetic diversity of lactococci isolated from raw milk in the Camembert cheese Registered Designation of Origin area was studied. Two seasonal samples (winter and summer) of raw milk were obtained from six farms in two areas (Bessin and Bocage Falaisien) of Normandy. All of the strains analyzed had a Lactococcus lactis subsp. lactis phenotype, whereas the randomly amplified polymorphic DNA (RAPD) technique genotypically identified the strains as members of L. lactis subsp. lactis or L. lactis subsp. cremoris. The genotypes were confirmed by performing standard PCR with primers corresponding to a region of the histidine biosynthesis operon. The geographic distribution of each subspecies of L. lactis was determined; 80% of the Bocage Falaisien strains were members of L. lactis subsp. lactis, and 30.5% of the Bessin strains were members of L. lactis subsp. lactis. A dendrogram was produced from a computer analysis of the RAPD profiles in order to evaluate the diversity of the lactococci below the subspecies level. The coefficient of similarity for 117 of the 139 strains identified as members of L. lactis subsp. cremoris was as high as 66%. The L. lactis subsp. lactis strains were more heterogeneous and formed 10 separate clusters (the level of similarity among the clusters was 18%). Reference strains of L. lactis subsp. lactis fell into 2 of these 10 clusters, demonstrating that lactococcal isolates are clearly different. As determined by the RAPD profiles, some L. lactis subsp. lactis strains were specific to the farms from which they originated and were recovered throughout the year (in both summer and winter). Therefore, the typicality of L. lactis subsp. lactis strains was linked to the farm of origin rather than the area. These findings emphasize the significance of designation of origin and the specificity of “Camembert de Normandie” cheese.     

Comparative genomic analysis of two Burkholderia glumae strains from different geographic origins reveals a high degree of plasticity in genome structure associated with genomic islands

Burkholderia glumae is the major causal agent of bacterial panicle blight of rice, a growing disease problem in global rice production. To better understand its genome-scale characteristics, the genome of the highly virulent B. glumae strain 336gr-1 isolated from Louisiana, USA was sequenced using the Illumina Genome Analyser II system. De novo assembled 336gr-1 contigs were aligned and compared with the previously sequenced genome of B. glumae strain BGR1, which was isolated from an infected rice plant in South Korea. Comparative analysis of the whole genomes of B. glumae 336gr-1 and B. glumae BGR1 revealed numerous unique genomic regions present only in one of the two strains. These unique regions contained accessory genes including mobile elements and phage-related genes, and some of the unique regions in B. glumae BGR1 corresponded to predicted genomic islands. In contrast, little variation was observed in known and potential virulence genes between the two genomes. The considerable amount of plasticity largely based on accessory genes and genome islands observed from the comparison of the genomes of these two strains of B. glumae may explain the versatility of this bacterial species in various environmental conditions and geographic locations.     

Genome sequence of Fusobacterium nucleatum subspecies polymorphum - a genetically tractable fusobacterium

Fusobacterium nucleatum is a prominent member of the oral microbiota and is a common cause of human infection. F. nucleatum includes five subspecies: polymorphum, nucleatum, vincentii, fusiforme, and animalis. F. nucleatum subsp. polymorphum ATCC 10953 has been well characterized phenotypically and, in contrast to previously sequenced strains, is amenable to gene transfer. We sequenced and annotated the 2,429,698 bp genome of F. nucleatum subsp. polymorphum ATCC 10953. Plasmid pFN3 from the strain was also sequenced and analyzed. When compared to the other two available fusobacterial genomes (F. nucleatum subsp. nucleatum, and F. nucleatum subsp. vincentii) 627 open reading frames unique to F. nucleatum subsp. polymorphum ATCC 10953 were identified. A large percentage of these mapped within one of 28 regions or islands containing five or more genes. Seventeen percent of the clustered proteins that demonstrated similarity were most similar to proteins from the clostridia, with others being most similar to proteins from other gram-positive organisms such as Bacillus and Streptococcus. A ten kilobase region homologous to the Salmonella typhimurium propanediol utilization locus was identified, as was a prophage and integrated conjugal plasmid. The genome contains five composite ribozyme/transposons, similar to the CdISt IStrons described in Clostridium difficile. IStrons are not present in the other fusobacterial genomes. These findings indicate that F. nucleatum subsp. polymorphum is proficient at horizontal gene transfer and that exchange with the Firmicutes, particularly the Clostridia, is common.     

Strain-Specific Genotyping of Bifidobacterium animalis subsp. lactis by Using Single-Nucleotide Polymorphisms,Insertions, and Deletions

Several probiotic strains of Bifidobacterium animalis subsp. lactis are widely supplemented into food products and dietary supplements due to their documented health benefits and ability to survive within the mammalian gastrointestinal tract and acidified dairy products. The strain specificity of these characteristics demands techniques with high discriminatory power to differentiate among strains. However, to date, molecular approaches, such as pulsed-field gel electrophoresis and randomly amplified polymorphic DNA-PCR, have been ineffective at achieving strain separation due to the monomorphic nature of this subspecies. Previously, sequencing and comparison of two B. animalis subsp. lactis genomes (DSMZ 10140 and Bl-04) confirmed this high level of sequence similarity, identifying only 47 single-nucleotide polymorphisms (SNPs) and four insertions and/or deletions (INDELs) between them. In this study, we hypothesized that a sequence-based typing method targeting these loci would permit greater discrimination between strains than previously attempted methods. Sequencing 50 of these loci in 24 strains of B. animalis subsp. lactis revealed that a combination of nine SNPs/INDELs could be used to differentiate strains into 14 distinct genotypic groups. In addition, the presence of a nonsynonymous SNP within the gene encoding a putative glucose uptake protein was found to correlate with the ability of certain strains to transport glucose and to grow rapidly in a medium containing glucose as the sole carbon source. The method reported here can be used in clinical, regulatory, and commercial applications requiring identification of B. animalis subsp. lactis at the strain level.Probiotics are currently defined as live microorganisms which, when administered in adequate amounts, confer a health benefit on the host (12). Many of the organisms studied for their probiotic potential are members of lactic acid bacteria and the genus Bifidobacterium, which has resulted in their inclusion in a large variety of dietary supplements and food products. Relative to most bifidobacterial species of human origin, Bifidobacterium animalis subsp. lactis is less sensitive to stressful conditions (bile, acid, and oxygen) which might be encountered in the mammalian gastrointestinal tract or in fermented or acidified dairy products (7, 26, 28, 31, 37). B. animalis subsp. lactis is widely added to commercial products because it is better able to withstand the adverse conditions of starter culture and product manufacture and to maintain viability and stability during product shelf-life (30). Therefore, strains of B. animalis, specifically B. animalis subsp. lactis, have been found in the majority of probiotic-supplemented dairy products surveyed in North America (the United States and Canada) and Europe (Great Britain, France, Italy, and Germany) (6, 13-15, 21, 22, 28, 29, 32, 49).When selecting a probiotic microorganism to add to supplements or foods, the strain must be identified at the genus, species, and strain levels (40). Proper characterization of a strain is important for safety and quality assurance, for identifying and differentiating putative probiotic strains, and for understanding the interactions among members of gut microbiota. In addition, proper characterization is important to maintain consumer confidence. Product labels often list invalid names of organisms or misidentify the species the product contains, leading to consumer confusion (6, 16, 20, 28, 29, 35, 38, 49). In the case of Bifidobacterium, most dairy products sold in the United States do not identify species, and many only refer to the invalid name “Bifid” or “Bifidus.” At the very least, added microorganisms should be accurately identified to the species level on product labels.According to the FAO/WHO guidelines for probiotic use, specific health benefits observed in research using a specific strain cannot be extrapolated to other, closely related strains (12). Although most clinical studies of probiotic strains compare strains of different genera or different species, few studies have assessed the actual variability of expected health benefits within species or subspecies. However, it is reasonable to consider that health effects, like the phenotypic traits exhibited by strains within a species, are strain specific. Therefore, reliable techniques for the identification of probiotic organisms at the strain level are required.Characterization to the strain level has several important potential applications. Understanding the complex interactions among microorganisms in the intestinal ecosystem requires methods of differentiating a strain of interest from other strains of the same species contained in the autochthonous microbiota. Strain differentiation techniques also aid in assessing survival of a probiotic organism through the gastrointestinal system, which is particularly important for clinical trials and regulatory purposes (17). The ability to uniquely identify a strain also lends credibility to statements made about the potential health benefits of consuming a particular product containing a strain with demonstrated probiotic effects and supports the licensing or intellectual property rights of the manufacturer.The high degree of genome conservation observed between strains of B. animalis subsp. lactis in terms of size, organization, and sequence is indicative of a genomically monomorphic subspecies (2, 25; also HN019 GenBank project 28807). As an example, comparison of the complete genome sequences of two B. animalis subsp. lactis strains, DSMZ 10140 (the type strain) and Bl-04 (a commercial strain, also known as RB 4825) (2), identified 47 single-nucleotide polymorphisms (SNPs) in nonrepetitive elements, as well as 443 bp distributed among four INDEL sites: a 121-bp tRNA-encoding sequence, a 54-bp region within the long-chain fatty acid-coenzyme A ligase gene, a 214-bp region within the CRISPR (clustered regularly interspaced short palindromic repeats) locus, and a 54-bp intergenic sequence. Overall, this 99.975% genome identity explains the inability to differentiate these strains by techniques such as the sequencing of housekeeping genes, multilocus sequence typing, and pulsed-field gel electrophoresis (PFGE) (3, 9, 23, 39, 44-46, 50).The strain specificity of reported health benefits of probiotics and the frequent use of B. animalis subsp. lactis as a probiotic in food products and supplements demands techniques with greater discriminatory power to identify and differentiate among strains within this highly homogeneous group. Unfortunately, strain level differentiation of B. animalis subsp. lactis presents several challenges. Although Ventura and Zink were able to differentiate strains of B. animalis subsp. lactis by sequencing the 16S-23S internal transcribed sequence (ITS) region (47), analysis of the four ITS operons between DSMZ 10140 and Bl-04 indicated complete identity (2). However, SNPs and INDELs do have potential for strain differentiation. According to Achtman, focusing on polymorphic SNPs is a desirable approach for the typing of monomorphic species (1). Therefore, the objective of the present study was to exploit the previously identified SNP and INDEL sites to develop a technique capable of differentiating among a collection of B. animalis subsp. lactis strains obtained from culture collections and commercial starter culture companies.     

Two binding proteins of the ABC transporter that confers growth of Bifidobacterium animalis subsp. lactis ATCC27673 on β‐mannan possess distinct manno‐oligosaccharide‐binding profiles

Human gut bifidobacteria rely on ATP‐binding cassette (ABC) transporters for oligosaccharide uptake. Multiple oligosaccharide‐specific solute‐binding protein (SBP) genes are occasionally associated with a single ABC transporter, but the significance of this multiplicity remains unclear. Here, we characterize BlMnBP1 and BlMnBP2, the two SBPs associated to the β‐manno‐oligosaccharide (MnOS) ABC transporter in Bifidobacterium animalis subsp. lactis. Despite similar overall specificity and preference to mannotriose (K_d≈80 nM), affinity of BlMnBP1 is up to 2570‐fold higher for disaccharides than BlMnBP2. Structural analysis revealed a substitution of an asparagine that recognizes the mannosyl at position 2 in BlMnBP1, by a glycine in BlMnBP2, which affects substrate affinity. Both substitution types occur in bifidobacterial SBPs, but BlMnBP1‐like variants prevail in human gut isolates. B. animalis subsp. lactis ATCC27673 showed growth on gluco and galactomannans and was able to outcompete a mannan‐degrading Bacteroides ovatus strain in co‐cultures, attesting the efficiency of this ABC uptake system. By contrast, a strain that lacks this transporter failed to grow on mannan. This study highlights SBP diversification as a possible strategy to modulate oligosaccharide uptake preferences of bifidobacterial ABC‐transporters during adaptation to specific ecological niches. Efficient metabolism of galactomannan by distinct bifidobacteria, merits evaluating this plant glycan as a potential prebiotic.     

A Single Mutation in the Gene Responsible for the Mucoid Phenotype of Bifidobacterium animalis subsp. lactis Confers Surface and Functional Characteristics

Exopolysaccharides (EPS) are extracellular carbohydrate polymers synthesized by a large variety of bacteria. Their physiological functions have been extensively studied, but many of their roles have not yet been elucidated. We have sequenced the genomes of two isogenic strains of Bifidobacterium animalis subsp. lactis that differ in their EPS-producing phenotype. The original strain displays a nonmucoid appearance, and the mutant derived thereof has acquired a mucoid phenotype. The sequence analysis of their genomes revealed a nonsynonymous mutation in the gene Balat_1410, putatively involved in the elongation of the EPS chain. By comparing a strain from which this gene had been deleted with strains containing the wild-type and mutated genes, we were able to show that each strain displays different cell surface characteristics. The mucoid EPS synthesized by the strain harboring the mutation in Balat_1410 provided higher resistance to gastrointestinal conditions and increased the capability for adhesion to human enterocytes. In addition, the cytokine profiles of human peripheral blood mononuclear cells and ex vivo colon tissues suggest that the mucoid strain could have higher anti-inflammatory activity. Our findings provide relevant data on the function of Balat_1410 and reveal that the mucoid phenotype is able to alter some of the most relevant functional properties of the cells.