Adaptation à l'environnement : métabolisme et communication bactérienne

Diplôme : HD

Clonage, caractérisation et analyse transcriptionnelle des gènes de la fermentation lactique chez Pediococcus acidilactici

Doctorat en sciences biologiques -- UCL, 199

Mutation of the oxaloacetate decarboxylase gene of Lactococcus lactis subsp. lactis impairs the growth during citrate metabolism

International audienceAims: Citrate metabolism generates metabolic energy through the generation of a membrane potential and a pH gradient. The purpose of this work was to study the influence of oxaloacetate decarboxylase in citrate metabolism and intracellular pH maintenance in relation to acidic conditions. Methods and Results: A Lactococcus lactis oxaloacetate decarboxylase mutant [ILCitM (pFL3)] was constructed by double homologous recombination. During culture with citrate, and whatever the initial pH, the growth rate of the mutant was lower. In addition, the production of diacetyl and acetoin was altered in the mutant strain. However, our results indicated no relationship with a change in the maintenance of intracellular pH. Experiments performed on resting cells clearly showed that oxaloacetate accumulated temporarily in the supernatant of the mutant. This accumulation could be involved in the perturbations observed during citrate metabolism, as the addition of oxaloacetate in M17 medium inhibited the growth of L. lactis. Conclusions: The mutation of oxaloacetate decarboxylase perturbed citrate metabolism and reduced the benefits of its utilization during growth under acidic conditions. Significance and impact of the study: This study allows a better understanding of citrate metabolism and the role of oxaloacetate decarboxylase in the tolerance of lactic acid bacteria to acidic conditions

Le système [i]agr[/i] de [i]Listeria monocytogenes[/i] et la croissance en biofilm : revisite des notions de communication, quorum sensing et auto-induction

Communication orale, résuméParmi les mécanismes cellulaires qui participent à la mise en place des biofilms, l’échange de molécules de communication apparaît nécessaire chez de nombreux microorganismes. Listeria monocytogenes est une bactérie ubiquiste responsable de pathologies sévères chez des populations à risque (immunodéprimés, femmes enceintes, personnes âgées) en cas de consommation d’aliments contaminés. Nous avons récemment démontré que le système de communication agr est impliqué au cours de la croissance sessile de cette bactérie (Rieu et al., 2007). Par ailleurs, l’expression du système agr était hétérogène pendant la croissance en biofilm (Rieu et al., 2008) et localisée à sa périphérie en conditions de flux continu. Cette observation va à l’encontre du paradigme du Quorum Sensing qui postule qu’une population de bactéries va développer une réponse concertée lorsque la molécule de communication atteint une concentration seuil. Afin d’étudier les notions de système auto-induit, de Quorum sensing et de communication chez Listeria monocytogenes, nous avons développé une approche combinant l’utilisation de systèmes rapporteurs de type gfp, la cytométrie de flux ainsi que des approches in situ de microscopie. Cette approche vise à étudier l’expression du système agr dans une population et de déterminer l’hétérogénéité de cette expression. La répartition de la fluorescence dans la population est comparée au cours de la croissance planctonique et sessile

Le système Agr de <em>Listeria monocytogenes</em> : revisite des notions de Quorum Sensing et auto-induction par cytométrie en flux

National audienc

<em>Listeria monocytogenes agr</em> system: Quorum sensing, or maybe not?

International audienc

Listeria monocytogenes, a down-to-earth pathogen

International audienceListeria monocytogenes is the causative agent of the food-borne life threatening disease listeriosis. This pathogenic bacterium received much attention in the endeavor of deciphering the cellular mechanisms that underlie the onset of infection and its ability to adapt to the food processing environment. Although information is available on the presence of L. monocytogenes in many environmental niches including soil, water, plants, foodstuff and animals, understanding the ecology of L. monocytogenes in outdoor environments has received less attention. Soil is an environmental niche of pivotal importance in the transmission of this bacterium to plants and animals. Soil composition, microbial communities and macrofauna are extrinsic edaphic factors that direct the fate of L. monocytogenes in the soil environment. Moreover, farming practices may further affect its incidence. The genome of L. monocytogenes presents an extensive repertoire of genes encoding transport proteins and regulators, a characteristic of the genome of ubiquitous bacteria. Postgenomic analyses bring new insights in the process of soil adaptation. In the present paper focussing on soil, we review these extrinsic and intrinsic factors that drive environmental adaptation of L. monocytogenes