Christophe Gitton

French National Institute for Agricultural Research, Lutetia Parisorum, Île-de-France, France

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Publications (15)51.52 Total impact

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    ABSTRACT: In streptococci, ComX is the alternative sigma factor controlling the transcription of the genes encoding the genetic transformation machinery. In Streptococcus thermophilus, comX transcription is controlled by a complex consisting of a transcriptional regulator of the Rgg family, ComR and a signaling peptide, ComS which controls ComR activity. Following its initial production, ComS is processed, secreted and imported back into the cell by the Ami oligopeptide transporter. We characterized these steps and the partners interacting with ComS during its extracellular circuit in more detail. We identified the mature form of ComS and demonstrated the involvement of the membrane protease Eep in ComS processing. We found that ComS was secreted, but probably not released into the extracellular medium. Natural competence was first discovered in a chemically defined medium without peptides. We show here that the presence of a high concentration of nutritional peptides in the medium prevents the triggering of competence. In milk, the ecological niche of S. thermophilus, competence was found to be functional, suggesting that the concentration of nutritional peptides was too low to interfere with ComR activation. The kinetics of expression of the comS, comR, and comX genes and of a late competence gene, dprA, in cultures inoculated at different initial densities, revealed that the activation mechanism of ComR by ComS is more a timing device rather than a quorum-sensing mechanism sensu stricto. We conclude that the ComS extracellular circuit facilitates tight control over the triggering of competence in S. thermophilus.
    Journal of bacteriology 02/2013; · 3.94 Impact Factor
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    ABSTRACT: Amino acid assimilation is crucial for bacteria and this is particularly true for Lactic Acid Bacteria (LAB) that are generally auxotroph for amino acids. The global response of the LAB model Lactococcus lactis ssp. lactis was characterized during progressive isoleucine starvation in batch culture using a chemically defined medium in which isoleucine concentration was fixed so as to become the sole limiting nutriment. Dynamic analyses were performed using transcriptomic and proteomic approaches and the results were analysed conjointly with fermentation kinetic data. The response was first deduced from transcriptomic analysis and corroborated by proteomic results. It occurred progressively and could be divided into three major mechanisms: (i) a global down-regulation of processes linked to bacterial growth and catabolism (transcription, translation, carbon metabolism and transport, pyrimidine and fatty acid metabolism), (ii) a specific positive response related to the limiting nutrient (activation of pathways of carbon or nitrogen metabolism and leading to isoleucine supply) and (iii) an unexpected oxidative stress response (positive regulation of aerobic metabolism, electron transport, thioredoxin metabolism and pyruvate dehydrogenase). The involvement of various regulatory mechanisms during this adaptation was analysed on the basis of transcriptomic data comparisons. The global regulator CodY seemed specifically dedicated to the regulation of isoleucine supply. Other regulations were massively related to growth rate and stringent response. This integrative biology approach provided an overview of the metabolic pathways involved during isoleucine starvation and their regulations. It has extended significantly the physiological understanding of the metabolism of L. lactis ssp. lactis. The approach can be generalised to other conditions and will contribute significantly to the identification of the biological processes involved in complex regulatory networks of micro-organisms.
    Microbial Cell Factories 08/2011; 10 Suppl 1:S18. · 3.31 Impact Factor
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    ABSTRACT: We identified a genetic context encoding a transcriptional regulator of the Rgg family and a small hydrophobic peptide (SHP) in nearly all streptococci and suggested that it may be involved in a new quorum-sensing mechanism, with SHP playing the role of a pheromone. Here, we provide further support for this hypothesis by constructing a phylogenetic tree of the Rgg and Rgg-like proteins from Gram-positive bacteria and by studying the shp/rgg1358 locus of Streptococcus thermophilus LMD-9. We identified the shp1358 gene as a target of Rgg1358, and used it to confirm the existence of the steps of a quorum-sensing mechanism including secretion, maturation and reimportation of the pheromone into the cell. We used surface plasmon resonance to demonstrate interaction between the pheromone and the regulatory protein and performed electrophoretic mobility shift assays to assess binding of the transcriptional regulator to the promoter regions of its target genes. The active form of the pheromone was identified by mass spectrometry. Our findings demonstrate that the shp/rgg1358 locus encodes two components of a novel quorum-sensing mechanism involving a transcriptional regulator of the Rgg family and a SHP pheromone that is detected and reimported into the cell by the Ami oligopeptide transporter.
    Molecular Microbiology 03/2011; 80(4):1102-19. · 4.96 Impact Factor
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    ABSTRACT: The thermophilic lactic acid bacterium Streptococcus thermophilus is widely and traditionally used in the dairy industry. Despite the vast level of consumption of S. thermophilus through yogurt or probiotic functional food, very few data are available about its physiology in the gastrointestinal tract (GIT). The objective of the present work was to explore both the metabolic activity and host response of S. thermophilus in vivo. Our study profiles the protein expression of S. thermophilus after its adaptation to the GIT of gnotobiotic rats and describes the impact of S. thermophilus colonization on the colonic epithelium. S. thermophilus colonized progressively the GIT of germ-free rats to reach a stable population in 30 days (10(8) cfu/g of feces). This progressive colonization suggested that S. thermophilus undergoes an adaptation process within GIT. Indeed, we showed that the main response of S. thermophilus in the rat's GIT was the massive induction of the glycolysis pathway, leading to formation of lactate in the cecum. At the level of the colonic epithelium, the abundance of monocarboxylic acid transporter mRNAs (SLC16A1 and SLC5A8) and a protein involved in the cell cycle arrest (p27(kip1)) increased in the presence of S. thermophilus compared with germ-free rats. Based on different mono-associated rats harboring two different strains of S. thermophilus (LMD-9 or LMG18311) or weak lactate-producing commensal bacteria (Bacteroides thetaiotaomicron and Ruminococcus gnavus), we propose that lactate could be a signal produced by S. thermophilus and modulating the colon epithelium.
    Journal of Biological Chemistry 01/2011; 286(12):10288-96. · 4.65 Impact Factor
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    ABSTRACT: Streptococcus thermophilus is the archetype of lactose-adapted bacterium and so far, its sugar metabolism has been mainly investigated in vitro. The objective of this work was to study the impact of lactose and lactose permease on S. thermophilus physiology in the gastrointestinal tract (GIT) of gnotobiotic rats. We used rats mono-associated with LMD-9 strain and receiving 4.5% lactose. This model allowed the analysis of colonization curves of LMD-9, its metabolic profile, its production of lactate and its interaction with the colon epithelium. Lactose induced a rapid and high level of S. thermophilus in the GIT, where its activity led to 49 mM of intra-luminal L-lactate that was related to the induction of mono-carboxylic transporter mRNAs (SLC16A1 and SLC5A8) and p27(Kip1) cell cycle arrest protein in epithelial cells. In the presence of a continuous lactose supply, S. thermophilus recruited proteins involved in glycolysis and induced the metabolism of alternative sugars as sucrose, galactose, and glycogen. Moreover, inactivation of the lactose transporter, LacS, delayed S. thermophilus colonization. Our results show i/that lactose constitutes a limiting factor for colonization of S. thermophilus, ii/that activation of enzymes involved in carbohydrate metabolism constitutes the metabolic signature of S. thermophilus in the GIT, iii/that the production of lactate settles the dialogue with colon epithelium. We propose a metabolic model of management of carbohydrate resources by S. thermophilus in the GIT. Our results are in accord with the rationale that nutritional allegation via consumption of yogurt alleviates the symptoms of lactose intolerance.
    PLoS ONE 01/2011; 6(12):e28789. · 3.73 Impact Factor
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    ABSTRACT: We characterized the insoluble proteome of Lactococcus lactis using 1D electrophoresis-LC-MS/MS and identified 313 proteins with at least two different peptides. The identified proteins include 89 proteins having a predicted signal peptide and 25 predicted to be membrane-located. In addition, 67 proteins had alkaline isoelectric point values. Using spectra and peptide counts, we compared protein abundances in two different conditions: growth in rich medium, and after transit in the mouse digestive tract. We identified the large mechanosensitive channel and a putative cation transporter as membrane markers of bacterial adaptation to the digestive tract.
    Journal of Proteome Research 12/2009; 9(2):677-88. · 5.06 Impact Factor
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    ABSTRACT: This genome-scale study analysed the various parameters influencing protein levels in cells. To achieve this goal, the model bacterium Lactococcus lactis was grown at steady state in continuous cultures at different growth rates, and proteomic and transcriptomic data were thoroughly compared. Ratios of mRNA to protein were highly variable among proteins but also, for a given gene, between the different growth conditions. The modeling of cellular processes combined with a data fitting modeling approach allowed both translation efficiencies and degradation rates to be estimated for each protein in each growth condition. Estimated translational efficiencies and degradation rates strongly differed between proteins and were tested for their biological significance through statistical correlations with relevant parameters such as codon or amino acid bias. These efficiencies and degradation rates were not constant in all growth conditions and were inversely proportional to the growth rate, indicating a more efficient translation at low growth rate but an antagonistic higher rate of protein degradation. Estimated protein median half-lives ranged from 23 to 224 min, underlying the importance of protein degradation notably at low growth rates. The regulation of intracellular protein level was analysed through regulatory coefficient calculations, revealing a complex control depending on protein and growth conditions. The modeling approach enabled translational efficiencies and protein degradation rates to be estimated, two biological parameters extremely difficult to determine experimentally and generally lacking in bacteria. This method is generic and can now be extended to other environments and/or other micro-organisms.
    PLoS Computational Biology 12/2009; 5(12):e1000606. · 4.87 Impact Factor
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    ABSTRACT: In gram-positive bacteria, oligopeptide transport systems, called Opp or Ami, play a role in nutrition but are also involved in the internalization of signaling peptides that take part in the functioning of quorum-sensing pathways. Our objective was to reveal functions that are controlled by Ami via quorum-sensing mechanisms in Streptococcus thermophilus, a nonpathogenic bacterium widely used in dairy technology in association with other bacteria. Using a label-free proteomic approach combining one-dimensional electrophoresis with liquid chromatography-tandem mass spectrometry analysis, we compared the proteome of the S. thermophilus LMD-9 to that of a mutant deleted for the subunits C, D, and E of the ami operon. Both strains were grown in a chemically defined medium (CDM) without peptides. We focused our attention on proteins that were no more detected in the ami deletion mutant. In addition to the three subunits of the Ami transporter, 17 proteins fulfilled this criterion and, among them, 7 were similar to proteins that have been identified as essential for transformation in S. pneumoniae. These results led us to find a condition of growth, the early exponential state in CDM, that allows natural transformation in S. thermophilus LMD-9 to turn on spontaneously. Cells were not competent in M17 rich medium. Furthermore, we demonstrated that the Ami transporter controls the triggering of the competence state through the control of the transcription of comX, itself controlling the transcription of late competence genes. We also showed that one of the two oligopeptide-binding proteins of strain LMD-9 plays the predominant role in the control of competence.
    Journal of bacteriology 06/2009; 191(14):4647-55. · 3.94 Impact Factor
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    ABSTRACT: Hydroxyacid dehydrogenases of lactic acid bacteria, which catalyze the stereospecific reduction of branched-chain 2-keto acids to 2-hydroxyacids, are of interest in a variety of fields, including cheese flavor formation via amino acid catabolism. In this study, we used both targeted and random mutagenesis to identify the genes responsible for the reduction of 2-keto acids derived from amino acids in Lactococcus lactis. The gene panE, whose inactivation suppressed hydroxyisocaproate dehydrogenase activity, was cloned and overexpressed in Escherichia coli, and the recombinant His-tagged fusion protein was purified and characterized. The gene annotated panE was the sole gene responsible for the reduction of the 2-keto acids derived from leucine, isoleucine, and valine, while ldh, encoding L-lactate dehydrogenase, was responsible for the reduction of the 2-keto acids derived from phenylalanine and methionine. The kinetic parameters of the His-tagged PanE showed the highest catalytic efficiencies with 2-ketoisocaproate, 2-ketomethylvalerate, 2-ketoisovalerate, and benzoylformate (V(max)/K(m) ratios of 6,640, 4,180, 3,300, and 2,050 U/mg/mM, respectively), with NADH as the exclusive coenzyme. For the reverse reaction, the enzyme accepted d-2-hydroxyacids but not l-2-hydroxyacids. Although PanE showed the highest degrees of identity to putative NADP-dependent 2-ketopantoate reductases (KPRs), it did not exhibit KPR activity. Sequence homology analysis revealed that, together with the d-mandelate dehydrogenase of Enterococcus faecium and probably other putative KPRs, PanE belongs to a new family of D-2-hydroxyacid dehydrogenases which is unrelated to the well-described D-2-hydroxyisocaproate dehydrogenase family. Its probable physiological role is to regenerate the NAD(+) necessary to catabolize branched-chain amino acids, leading to the production of ATP and aroma compounds.
    Journal of bacteriology 01/2009; 191(3):873-81. · 3.94 Impact Factor
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    ABSTRACT: We have compared the proteomic profiles of L. lactis subsp. cremoris NCDO763 growing in the synthetic medium M17Lac, skim milk microfiltrate (SMM), and skim milk. SMM was used as a simple model medium to reproduce the initial phase of growth of L. lactis in milk. To widen the analysis of the cytoplasmic proteome, we used two different gel systems (pH ranges of 4 to 7 and 4.5 to 5.5), and the proteins associated with the cell envelopes were also studied by two-dimensional electrophoresis. In the course of the study, we analyzed about 800 spots and identified 330 proteins by mass spectrometry. We observed that the levels of more than 50 and 30 proteins were significantly increased upon growth in SMM and milk, respectively. The large redeployment of protein synthesis was essentially associated with an activation of pathways involved in the metabolism of nitrogenous compounds: peptidolytic and peptide transport systems, amino acid biosynthesis and interconversion, and de novo biosynthesis of purines. We also showed that enzymes involved in reactions feeding the purine biosynthetic pathway in one-carbon units and amino acids have an increased level in SMM and milk. The analysis of the proteomic data suggested that the glutamine synthetase (GS) would play a pivotal role in the adaptation to SMM and milk. The analysis of glnA expression during growth in milk and the construction of a glnA-defective mutant confirmed that GS is an essential enzyme for the development of L. lactis in dairy media. This analysis thus provides a proteomic signature of L. lactis, a model lactic acid bacterium, growing in its technological environment.
    Applied and Environmental Microbiology 12/2005; 71(11):7152-63. · 3.68 Impact Factor
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    ABSTRACT: Summary Proteomic analysis is intrinsically an iterative, incremental process. Information is usually acquired gradually by researchers, and in different projects. At the same time, there are rel- atively few examples of biological data management systems which take into account this reality, most of them usually treat the experiment generated data as static and unchange- able: data are never reconsidered, or seldom, whereas technology becomes more power- ful or that other researchers have brought information on data correction. And yet, post- planned analysis (21) which involves multiple iterations and subsequent re-investigations of previously prepared data might bring tremendous benefits. Named PARIS (Proteomic Analysis and Resources Indexation System), the system we developed here seeks to address this requirement. Compliant with the majority of 2-DE analysis and MALDI-TOF based protein identification softwares, it automatically takes data from them and stores the raw and processed data in a relational database suitable for advanced exploration. Taking into account the standards proposed by PSI (Proteomics Standard Initiative), the system exports the stored data in XML format for data exchange and knowledge sharing. PARIS also manages information about experiments and their biological contexts, and allows the user to search and analyze a large data collection in a global manner. It provides tools for data integration and advanced, cross multi-experiment, multi-experimenter data exploration, and supports visual verification and correction of the analysis results. Implemented in Java, the system is platform independent, accessible to multiple users through Internet. It is also scalable for use for one or many laboratories, and therefore suitable to inter-institute collaborative work. PARIS can be tested and downloaded athttp://genome.jouy.inra.fr/paris
    Journal of integrative bioinformatics 01/2005; 2(1).
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    ABSTRACT: We developed a system for managing data from two-dimensional electrophoresis-based proteomic experiments. Named PARIS, the system stores gel image and information about experiments and analysis procedures, allows the user to search and navigate in genomic and proteomic data, supports visual verification and validation of the analysis results, and provides tools for cross multi-experiment and multi-experimenter data validation and exploration. AVAILABILITY: The software is freely available from http://www.inra.fr/bia/J/imaste/Projets/PARIS/index.html
    Bioinformatics 02/2004; 20(1):133-5. · 5.32 Impact Factor
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    ABSTRACT: f the data. The system is not a data library any more but a resource and knowledge ware that makes us be able to confront data from different experiments and use previous results to help investigating recent data (or use new results to re-investigate previously prepared gel). Given a spot, we will thus have access to the list of the spots with which it was connected in other experiments, therefore summarizing work of many people and produced from multiple projects. This also makes it possible to distribute new knowledge quickly, one can submit his results to the ware as soon as new information is discovered. Relying on these observations, we begin to develop a general-purpose integrated proteomic analysis and resources management system. Named PARIS (Proteomic Analysis and Resources Indexation System), the proposed system integrates the above-mentioned three issues in a processing unit. It stores gel image and information about experiments and analysis procedure, allows the user to se
    06/2003;
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    ABSTRACT: Lactococcus lactis is a Gram-positive bacteria, which belongs to the group of lactic acid bacteria among which several genera play an essential role in the manufacture of food products. Cytosolic proteins of L. lactis IL1403 cultivated in M17 broth have been resolved by two-dimensional gel electrophoresis using two pH gradients (pH 4-7, 4.5-5.5). More than 230 spots were identified by peptide mass fingerprints, corresponding to 25% of the predicted acid proteome. The present study made it possible to describe at the proteome level a significant number of cellular pathways (glycolysis, fermentation, nucleotide metabolism, proteolysis, fatty acid and peptidoglycan synthesis) related to important physiological processes and technological properties. It also indicated that the fermentative metabolism, which characterizes L. lactis is associated with a high expression of glycolytic enzymes. Thirty-four proteins were matched to open reading frames for which there is no assigned function. The comparison at the proteome level of two strains of L. lactis showed an important protein polymorphism. The comparison of the proteomes of glucose- and lactose-grown cells revealed an unexpected link between the nature of the carbon source and the metabolism of pyrimidine nucleotides.
    PROTEOMICS 04/2003; 3(3):337-54. · 4.13 Impact Factor
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    ABSTRACT: Proteomic analysis is intrinsically an iterative, incremental process. Information is usually acquired gradually by researchers, and in different projects. At the same time, there are relatively few examples of biological data management systems which take into account this reality, most of them usually treat the experiment generated data as static and unchangeable: data are never reconsidered, or seldom, whereas technology becomes more powerful or that other researchers have brought information on data correction. And yet, postplanned analysis which involves multiple iterations and subsequent re-investigations of previously prepared data might bring tremendous benefits. Named PARIS (Proteomic Analysis and Resources Indexation System), the system we developed here seeks to address this requirement. Compliant with the majority of 2-DE analysis and MALDI-TOF based protein identification softwares, it automatically takes data from them and stores the raw and processed data in a relational database suitable for advanced exploration. Taking into account the standards proposed by PSI (Proteomics Standard Initiative), the system exports the stored data in XML format for data exchange and knowledge sharing. PARIS also manages information about experiments and their biological contexts, and allows the user to search and analyze a large data collection in a global manner. It provides tools for data integration and advanced, cross multi-experiment, multi-experimenter data exploration, and supports visual verification and correction of the analysis results. Implemented in Java, the system is platform independent, accessible to multiple users through Internet. It is also scalable for use for one or many laboratories, and therefore suitable to inter-institute collaborative work.
    http://journal.imbio.de/index.php?paper_id=12.