Birgitte Stuer-Lauridsen

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

ABSTRACT 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 cells physiology.

Identification of Lactococcus lactis Genes Required for Bacteriophage Adsorption

ABSTRACT The aim of this work was to identify genes in Lactococcus lactis subsp. lactis IL1403 and Lactococcus lactis subsp. cremoris Wg2 important for adsorption of the 936-species phages bIL170 and φ645, respectively. Random insertional mutagenesis of the two L. lactis strains was carried out with the vector pGh9:ISS1, and integrants that were resistant to phage infection and showed reduced phage adsorption were selected. In L. lactis IL1403 integration was obtained in the ycaG and rgpE genes, whereas in L. lactis Wg2 integration was obtained in two genes homologous to ycbC and ycbB of L. lactis IL1403. rgpE and ycbB encode putative glycosyltransferases, whereas ycaG and ycbC encode putative membrane-spanning proteins with unknown functions. Interestingly, ycaG, rgpE, ycbC, and ycbB are all part of the same operon in L. lactis IL1403. This operon is probably involved in biosynthesis and transport of cell wall polysaccharides (WPS). Binding and infection studies showed that φ645 binds to and infects L. lactis Wg2, L. lactis IL1403, and L. lactis IL1403 strains with pGh9:ISS1 integration in ycaG and rgpE, whereas bIL170 binds to and infects only L. lactis IL1403 and cannot infect Wg2. These results indicate that φ645 binds to a WPS structure present in both L. lactis IL1403 and L. lactis Wg2, whereas bIL170 binds to another WPS structure not present in L. lactis Wg2. Binding of bIL170 and φ645 to different WPS structures was supported by alignment of the receptor-binding proteins of bIL170 and φ645 that showed no homology in the C-terminal part.

The extracellular proteome of Bifidobacterium animalis subsp. lactis BB-12 reveals proteins with putative roles in probiotic effects

Probiotics are live microorganisms that exert health‐promoting effects on the human host, as demonstrated for numerous strains of the genus Bifidobacterium. To unravel the proteins involved in the interactions between the host and the extensively used and well‐studied probiotic strain Bifidobacterium animalis subsp. lactis BB‐12, proteins secreted by the bacterium, i.e. belonging to the extracellular proteome present in the culture medium, were identified by 2‐DE coupled with MALDI‐TOF MS. Among the 74 distinct proteins identified, 31 are predicted to carry out their physiological role either outside the cell or on its surface. These proteins include solute‐binding proteins for oligosaccharides, amino acids and manganese, cell wall‐metabolizing proteins, and 18 proteins that have been described to interact with human host epithelial cells or extracellular matrix proteins. The potential functions include binding of plasminogen, formation of fimbriae, adhesion to collagen, attachment to mucin and intestinal cells as well as induction of immunomodulative response. These findings suggest a role of the proteins in colonization of the gastrointestinal tract, adhesion to host tissues, or immunomodulation of the host immune system. The identification of proteins predicted to be involved in such interactions can pave the way towards well targeted studies of the protein‐mediated contacts between bacteria and the host, with the goal to enhance the understanding of the mode of action of probiotic bacteria.

Combined Transcriptome and Proteome Analysis of Bifidobacterium animalis subsp. lactis BB-12 Grown on Xylo-Oligosaccharides and a Model of Their Utilization†

ABSTRACT Recent studies have demonstrated that xylo-oligosaccharides (XOS), which are classified as emerging prebiotics, selectively enhance the growth of bifidobacteria in general and of Bifidobacteriumanimalis subsp. lactis strains in particular. To elucidate the metabolism of XOS in the well-documented and widely used probiotic strain B. animalis subsp. lactis BB-12, a combined proteomic and transcriptomic approach was applied, involving DNA microarrays, real-time quantitative PCR (qPCR), and two-dimensional difference gel electrophoresis (2D-DIGE) analyses of samples obtained from cultures grown on either XOS or glucose. The analyses show that 9 of the 10 genes that encode proteins predicted to play a role in XOS catabolism (i.e., XOS-degrading and -metabolizing enzymes, transport proteins, and a regulatory protein) were induced by XOS at the transcriptional level, and the proteins encoded by three of these (β-d-xylosidase, sugar-binding protein, and xylose isomerase) showed higher abundance on XOS. Based on the obtained results, a model for the catabolism of XOS in BB-12 is suggested, according to which the strain utilizes an ABC (ATP-binding cassette) transport system (probably for oligosaccharides) to bind XOS on the cell surface and transport them into the cell. XOS are then degraded intracellularly through the action of xylanases and xylosidases to d-xylose, which is subsequently metabolized by the d-fructose-6-P shunt. The findings obtained in this study may have implications for the design of a synbiotic application containing BB-12 and the XOS used in the present study.

Identification of the host determinant of two prolate-headed phages infecting lactococcus lactis

A gene responsible for host determination was identified in two prolate-headed bacteriophages of the c2 species infecting strains of Lactococcus lactis. The identification of the host determinant gene was based on low DNA sequence homology in a specific open reading frame (ORF) between prolate-headed phages with different host ranges. When a host carrying this ORF from one phage on a plasmid was infected with another phage, we obtained phages with an altered host range at a frequency of 10(-6) to 10(-7). Sequencing of phage DNA originating from 10 independent single plaques confirmed that a genetic recombination had taken place at different positions between the ORF on the plasmid and the infecting phage. The adsorption of the recombinant phages to their bacterial hosts had also changed to match the phage origin of the ORF. Consequently, it is concluded that this ORF codes for the host range determinant.

The Science behind the Probiotic Strain Bifidobacterium animalis subsp. lactis BB-12 ®

This review presents selected data on the probiotic strain Bifidobacterium animalis subsp. lactis BB-12® (BB-12®), which is the world’s most documented probiotic Bifidobacterium. It is described in more than 300 scientific publications out of which more than 130 are publications of human clinical studies. The complete genome sequence of BB-12® has been determined and published. BB-12® originates from Chr. Hansen’s collection of dairy cultures and has high stability in foods and as freeze dried powders. Strain characteristics and mechanisms of BB-12® have been established through extensive in vitro testing. BB-12® exhibits excellent gastric acid and bile tolerance; it contains bile salt hydrolase, and has strong mucus adherence properties, all valuable probiotic characteristics. Pathogen inhibition, barrier function enhancement, and immune interactions are mechanisms that all have been demonstrated for BB-12®. BB-12® has proven its beneficial health effect in numerous clinical studies within gastrointestinal health and immune function. Clinical studies have demonstrated survival of BB-12® through the gastrointestinal tract and BB-12® has been shown to support a healthy gastrointestinal microbiota. Furthermore, BB-12® has been shown to improve bowel function, to have a protective effect against diarrhea, and to reduce side effects of antibiotic treatment, such as antibiotic-associated diarrhea. In terms of immune function, clinical studies have shown that BB-12® increases the body’s resistance to common respiratory infections as well as reduces the incidence of acute respiratory tract infections.

Screening for Antimicrobial Resistance Genes and Virulence Factors via Genome Sequencing

ABSTRACT Second-generation genome sequencing and alignment of the resulting reads to in silico genomes containing antimicrobial resistance and virulence factor genes were used to screen for undesirable genes in 28 strains which could be used in human nutrition. No virulence factor genes were detected, while several isolates contained antimicrobial resistance genes.

The art of strain improvement of industrial lactic acid bacteria without the use of recombinant DNA technology

The food industry is constantly striving to develop new products to fulfil the ever changing demands of consumers and the strict requirements of regulatory agencies. For foods based on microbial fermentation, this pushes the boundaries of microbial performance and requires the constant development of new starter cultures with novel properties. Since the use of ingredients in the food industry is tightly regulated and under close scrutiny by consumers, the use of recombinant DNA technology to improve microbial performance is currently not an option. As a result, the focus for improving strains for microbial fermentation is on classical strain improvement methods. Here we review the use of these techniques to improve the functionality of lactic acid bacteria starter cultures for application in industrial-scale food production. Methods will be described for improving the bacteriophage resistance of specific strains, improving their texture forming ability, increasing their tolerance to stress and modulating both the amount and identity of acids produced during fermentation. In addition, approaches to eliminating undesirable properties will be described. Techniques include random mutagenesis, directed evolution and dominant selection schemes.

Genetic Basis of Tetracycline Resistance in Bifidobacterium animalis subsp lactis

ABSTRACT All strains of Bifidobacterium animalis subsp. lactis described to date show medium level resistance to tetracycline. Screening of 26 strains from a variety of sources revealed the presence of tet(W) in all isolates. A transposase gene upstream of tet(W) was found in all strains, and both genes were cotranscribed in strain IPLAIC4. Mutants with increased tetracycline resistance as well as tetracycline-sensitive mutants of IPLAIC4 were isolated and genetically characterized. The native tet(W) gene was able to restore the resistance phenotype to a mutant with an alteration in tet(W) by functional complementation, indicating that tet(W) is necessary and sufficient for the tetracycline resistance seen in B. animalis subsp. lactis.

Antimicrobial Susceptibility of Bacillus Strains Isolated from Primary Starters for African Traditional Bread Production and Characterization of the Bacitracin Operon and Bacitracin Biosynthesis

ABSTRACT Bacillus spp. are widely used as feed additives and probiotics. However, there is limited information on their resistance to various antibiotics, and there is a growing concern over the transfer of antibiotic resistance genes. The MIC for 8 antibiotics was determined for 85 Bacillus species strains, Bacillus subtilis subsp. subtilis (n = 29), Bacillus licheniformis (n = 38), and Bacillus sonorensis (n = 18), all of which were isolated from starters for Sudanese bread production. All the strains were sensitive to tetracycline (8.0 mg/liter), vancomycin (4.0 mg/liter), and gentamicin (4.0 mg/liter) but resistant to streptomycin. Sensitivity to clindamycin, chloramphenicol, and kanamycin was species specific. The erythromycin resistance genes ermD and ermK were detected by PCR in all of the erythromycin-resistant (MIC, ≥16.0 mg/liter) B. licheniformis strains and one erythromycin-sensitive (MIC, 4.0 mg/liter) B. licheniformis strain. Several amino acid changes were present in the translated ermD and ermK nucleotide sequences of the erythromycin-sensitive strain, which could indicate ErmD and ErmK protein functionalities different from those of the resistance strains. The ermD and ermK genes were localized on an 11.4-kbp plasmid. All of the B. sonorensis strains harbored the bacitracin synthetase gene, bacA, and the transporter gene bcrA, which correlated with their observed resistance to bacitracin. Bacitracin was produced by all the investigated species strains (28%), as determined by ultra-high-definition quadrupole time-of-flight liquid chromatography-mass spectrometry (UHD-QTOF LC/MS). The present study has revealed species-specific variations in the antimicrobial susceptibilities of Bacillus spp. and provides new information on MIC values, as well as the occurrence of resistance genes in Bacillus spp., including the newly described species B. sonorensis.