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1.  Commensal Streptococcus salivarius Modulates PPARγ Transcriptional Activity in Human Intestinal Epithelial Cells 
PLoS ONE  2015;10(5):e0125371.
The impact of commensal bacteria in eukaryotic transcriptional regulation has increasingly been demonstrated over the last decades. A multitude of studies have shown direct effects of commensal bacteria from local transcriptional activity to systemic impact. The commensal bacterium Streptococcus salivarius is one of the early bacteria colonizing the oral and gut mucosal surfaces. It has been shown to down-regulate nuclear transcription factor (NF-кB) in human intestinal cells, a central regulator of the host mucosal immune system response to the microbiota. In order to evaluate its impact on a further important transcription factor shown to link metabolism and inflammation in the intestine, namely PPARγ (peroxisome proliferator-activated receptor), we used human intestinal epithelial cell-lines engineered to monitor PPARγ transcriptional activity in response to a wide range of S. salivarius strains. We demonstrated that different strains from this bacterial group share the property to inhibit PPARγ activation independently of the ligand used. First attempts to identify the nature of the active compounds showed that it is a low-molecular-weight, DNase-, proteases- and heat-resistant metabolite secreted by S. salivarius strains. Among PPARγ-targeted metabolic genes, I-FABP and Angptl4 expression levels were dramatically reduced in intestinal epithelial cells exposed to S. salivarius supernatant. Both gene products modulate lipid accumulation in cells and down-regulating their expression might consequently affect host health. Our study shows that species belonging to the salivarius group of streptococci impact both host inflammatory and metabolic regulation suggesting a possible role in the host homeostasis and health.
PMCID: PMC4422599  PMID: 25946041
2.  A Robust and Adaptable High Throughput Screening Method to Study Host-Microbiota Interactions in the Human Intestine 
PLoS ONE  2014;9(8):e105598.
The intestinal microbiota has many beneficial roles for its host. However, the precise mechanisms developed by the microbiota to influence the host intestinal cell responses are only partially known. The complexity of the ecosystem and our inability to culture most of these micro-organisms have led to the development of molecular approaches such as functional metagenomics, i.e. the heterologous expression of a metagenome in order to identify functions. This elegant strategy coupled to high throughput screening allowed to identify novel enzymes from different ecosystems where culture methods have not yet been adapted to isolate the candidate microorganisms. We have proposed to use this functional metagenomic approach in order to model the microbiota’s interaction with the host by combining this heterologous expression with intestinal reporter cell lines. The addition of the cellular component to this functional metagenomic approach introduced a second important source of variability resulting in a novel challenge for high throughput screening. First attempts of high throughput screening with various reporter cell-lines showed a high distribution of the response and consequent difficulties to reproduce the response, impairing an easy and clear identification of confirmed hits. In this study, we developed a robust and reproducible methodology to combine these two biological systems for high throughput application. We optimized experimental setups and completed them by appropriate statistical analysis tools allowing the use this innovative approach in a high throughput manner and on a broad range of reporter assays. We herewith present a methodology allowing a high throughput screening combining two biological systems. Therefore ideal conditions for homogeneity, sensitivity and reproducibility of both metagenomic clones as well as reporter cell lines have been identified and validated. We believe that this innovative method will allow the identification of new bioactive microbial molecules and, subsequently, will promote understanding of host-microbiota interactions.
PMCID: PMC4139392  PMID: 25141006
3.  Genome Sequence of “Candidatus Arthromitus” sp. Strain SFB-Mouse-NL, a Commensal Bacterium with a Key Role in Postnatal Maturation of Gut Immune Functions 
Genome Announcements  2014;2(4):e00705-14.
“Candidatus Arthromitus” sp. strain SFB-mouse-NL (SFB, segmented filamentous bacteria) is a commensal bacterium necessary for inducing the postnatal maturation of homeostatic innate and adaptive immune responses in the mouse gut. Here, we report the genome sequence of this bacterium, which sets it apart from earlier sequenced mouse SFB isolates.
PMCID: PMC4102870  PMID: 25035333
4.  High-Throughput System for the Presentation of Secreted and Surface-Exposed Proteins from Gram-Positive Bacteria in Functional Metagenomics Studies 
PLoS ONE  2013;8(6):e65956.
Complex microbial ecosystems are increasingly studied through the use of metagenomics approaches. Overwhelming amounts of DNA sequence data are generated to describe the ecosystems, and allow to search for correlations between gene occurrence and clinical (e.g. in studies of the gut microbiota), physico-chemical (e.g. in studies of soil or water environments), or other parameters. Observed correlations can then be used to formulate hypotheses concerning microbial gene functions in relation to the ecosystem studied. In this context, functional metagenomics studies aim to validate these hypotheses and to explore the mechanisms involved. One possible approach is to PCR amplify or chemically synthesize genes of interest and to express them in a suitable host in order to study their function. For bacterial genes, Escherichia coli is often used as the expression host but, depending on the origin and nature of the genes of interest and the test system used to evaluate their putative function, other expression systems may be preferable. In this study, we developed a system to evaluate the role of secreted and surface-exposed proteins from Gram-positive bacteria in the human gut microbiota in immune modulation. We chose to use a Gram-positive host bacterium, Bacillus subtilis, and modified it to provide an expression background that behaves neutral in a cell-based immune modulation assay, in vitro. We also adapted an E. coli – B. subtilis shuttle expression vector for use with the Gateway high-throughput cloning system. Finally, we demonstrate the functionality of this host-vector system through the cloning and expression of a flagellin-coding sequence, and show that the expression-clone elicits an inflammatory response in a human intestinal epithelial cell line. The expression host can easily be adapted to assure neutrality in other assay systems, allowing the use of the presented presentation system in functional metagenomics of the gut and other ecosystems.
PMCID: PMC3682982  PMID: 23799065
5.  Identification of NF-κB Modulation Capabilities within Human Intestinal Commensal Bacteria 
The intestinal microbiota plays an important role in modulation of mucosal immune responses. To seek interactions between intestinal epithelial cells (IEC) and commensal bacteria, we screened 49 commensal strains for their capacity to modulate NF-κB. We used HT-29/kb-seap-25 and Caco-2/kb-seap-7 intestinal epithelial cells and monocyte-like THP-1 blue reporter cells to measure effects of commensal bacteria on cellular expression of a reporter system for NF-κB. Bacteria conditioned media (CM) were tested alone or together with an activator of NF-κB to explore its inhibitory potentials. CM from 8 or 10 different commensal species activated NF-κB expression on HT-29 and Caco-2 cells, respectively. On THP-1, CM from all but 5 commensal strains stimulated NF-κB. Upon challenge with TNF-α or IL-1β, some CM prevented induced NF-κB activation, whereas others enhanced it. Interestingly, the enhancing effect of some CM was correlated with the presence of butyrate and propionate. Characterization of the effects of the identified bacteria and their implications in human health awaits further investigations.
PMCID: PMC3134244  PMID: 21765633
6.  Reporter bacteriophage A511::celB transduces a hyperthermostable glycosidase from Pyrococcus furiosus for rapid and simple detection of viable Listeria cells 
Bacteriophage  2011;1(3):143-151.
Reporter bacteriophages for detection of pathogenic bacteria offer fast and sensitive screening for live bacterial targets. We present a novel strategy employing a gene encoding a hyperthermophilic enzyme, permitting the use of various substrates and assay formats. The celB gene from the hyperthermophilic archaeon Pyrococcus furiosus specifying an extremely thermostable β-glycosidase was inserted into the genome of the broad host range, virulent Listeria phage A511 by homologous recombination. It is expressed at the end of the infectious cycle, under control of the strong major capsid gene promoter Pcps. Infection of Listeria with A511::celB results in strong gene expression and synthesis of a fully functional β-glycosidase. The reporter phage was tested for detection of viable Listeria cells with different chromogenic, fluorescent or chemiluminescent substrates. The best signal-to-noise ratio and sufficiently high sensitivity was obtained using the inexpensive substrate 4-Methylumbelliferyl-α-D-Glucopyranoside (MUG). The reporter phage assay is simple to perform and can be completed in about 6 h. Phage infection, as well as the subsequent temperature shift, enzymatic substrate conversion and signal recordings are independent from each other and may be performed separately. The detection limit for viable Listeria monocytogenes in an assay format adapted to 96-well microplates was 7.2 × 102 cells per well, corresponding to 6 × 103 cfu per ml in suspension. Application of the A511::celB protocol to Listeria in spiked chocolate milk and salmon demonstrate the usefulness of the reporter phage for rapid detection of low numbers of the bacteria (10 cfu/g or less) in contaminated foods.
PMCID: PMC3225779  PMID: 22164348
Listeria monocytogenes; reporter bacteriophage; Pyrococcus furiosus; glycosidase; celB; rapid methods; food safety

Results 1-6 (6)