LptM promotes oxidative maturation of the lipopolysaccharide translocon by substrate binding mimicry

Insertion of lipopolysaccharide (LPS) into the bacterial outer membrane (OM) is mediated by a druggable OM translocon consisting of a β-barrel membrane protein, LptD, and a lipoprotein, LptE. The β-barrel assembly machinery (BAM) assembles LptD together with LptE at the OM. In the enterobacterium Escherichia coli, formation of two native disulfide bonds in LptD controls translocon activation. Here we report the discovery of LptM (formerly YifL), a lipoprotein conserved in Enterobacteriaceae, that assembles together with LptD and LptE at the BAM complex. LptM stabilizes a conformation of LptD that can efficiently acquire native disulfide bonds, whereas its inactivation makes disulfide bond isomerization by DsbC become essential for viability. Our structural prediction and biochemical analyses indicate that LptM binds to sites in both LptD and LptE that are proposed to coordinate LPS insertion into the OM. These results suggest that, by mimicking LPS binding, LptM facilitates oxidative maturation of LptD, thereby activating the LPS translocon

Study of a microbial consortium producing hydrogen : from the inter-bacterial interaction to bioreactor

Dans la nature, les microorganismes s’organisent en communauté où la concertation de leur métabolisme leur permet de coloniser des endroits peu propices. La biodégradation de la matière organique nécessite un couplage métabolique entre les différents microorganismes impliqués et constitue un modèle de choix pour l'étude des interactions où leurs relations restent mal définies et nécessitent d’être mieux caractérisées. Le décryptage du mécanisme mis en jeu permettrait d'optimiser la production de composés bioénergétiques comme l'hydrogène. Nous avons étudié un consortium composé de Desulfovibris vulgaris Hildenborough, une bactérie sulfato-réductrice et de Clostridium acetobutylicum, une bactérie fermentaire. Ces deux bactéries sont retrouvées dans des consortia naturels impliqués dans la dégradation de la biomasse. Des approches de microbiologie, de métabolisme et de microscopie ont permis de démontrer l’existence d’une interaction physique et d'un échange de molécules cytoplasmiques entre les deux bactéries. Ceci s'associe à une réorientation du flux de carbone dans la bactérie C. acetobutylicum qui se traduit par une production d’hydrogène accrue. Ce comportement est lié aux conditions de stress nutritionnel pour la bactérie D. vulgaris. De plus, des molécules signal de type AI-2 jouent un rôle important dans la mise place de l'interaction physique. Un inhibiteur de cette interaction, produit par D. vulgaris dans certaines conditions, a été découvert. Ce travail a permis d'acquérir de nouvelles connaissances sur les relations métaboliques et les interactions physiques entre les bactéries impliquées dans la biodégradation de la biomasse dans un consortium.In nature microorganisms live in communities, in which the complementarity of their metabolism allows them to colonize less favourable ecological niches. Biodegradation of organic matter requires tight metabolic coupling between the different microorganisms involved, and constitutes an ideal model for studying the interactions between them, which are still not well established and require further characterization. Furthermore, deciphering the metabolic couplings established between the partners would allow optimization of this process for production of compounds of biotechnological interest, such as hydrogen. During the course of this work we have studied an artificial consortium constituted by Desulfovibris vulgaris Hildenborough sulphate-reducing bacterium, and Clostridium acetobutylicum a fermentative bacterium; both of them are found in natural consortia involved in biomass degradation. Microbiological, metabolic and microscopic approaches allowed us to show the existence of a physical interaction, with exchange of cytoplasmic molecules, between the two bacteria. This is associated with reorientation of the carbon flux in Clostridium acetobutylicum, resulting in increased hydrogen production. This behaviour is linked with the nutritional stress of D. vulgaris. Moreover, AI-2 type signal molecules produced in these conditions are crucial for the physical interaction between the two bacterial partners. An inhibitor produced by D. vulgaris in certain conditions has been discovered. This work has allowed us to acquire new knowledge about metabolic relations and physical interactions between bacteria involved in biomass degradation in a consortiu

Characterization of RV1683, a bifunctional enzyme involved in storage and mobilization of mycobacterial lipid droplets

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Bacterial machineries for the assembly of membrane-embedded β-barrel proteins

International audienc

Impact on Hydrogen Metabolism of physical interactions between Desulfovibrio and Clostridium

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Anaerobic biofilm reactors for dark fermentative hydrogen production from wastewater: A review

International audienceDark fermentation is a bioprocess driven by anaerobic bacteria that can produce hydrogen (H2) from organic waste and wastewater. This review analyses a relevant number of recent studies that have investigated dark fermentative H2 production from wastewater using two different types of anaerobic biofilm reactors: anaerobic packed bed reactor (APBR) and anaerobic fluidized bed reactor (AFBR). The effect of various parameters, including temperature, pH, carrier material, inoculum pretreatment, hydraulic retention time, substrate type and concentration, on reactor performances was investigated by a critical discussion of the results published in the literature. Also, this review presents an in-depth study on the influence of the main operating parameters on the metabolic pathways. The aim of this review is to provide to researchers and practitioners in the field of H2 production key elements for the best operation of the reactors. Finally, some perspectives and technical challenges to improve H2 production were proposed

Dark fermentative hydrogen production in an anaerobic packed bed biofilm reactor

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Fermentative hydrogen production using a co-culture of C. acetobutylicum and D. vulgaris: an interdisciplinary approach from batch to continuous flow biofilm reactors

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Fermentative hydrogen production in an up-flow anaerobic biofilm reactor inoculated with a co-culture of Clostridium acetobutylicum and Desulfovibrio vulgaris

International audienceDark fermentation systems often show low H2 yields and unstable H2 production, as the result of the variability of microbial dynamics and metabolic pathways. Recent batch investigations have demonstrated that an artificial consortium of two anaerobic bacteria, Clostridium acetobutylicum and Desulfovibrio vulgaris Hildenborough, may redirect metabolic fluxes and improve H2 yields. This study aimed at evaluating the scale-up from batch to continuous H2 production in an up-flow anaerobic packed-bed reactor (APBR) continuously fed with a glucose-medium. The effects of various parameters, including void hydraulic retention time (HRTv), pH, and alkalinity, on H2 production performances and metabolic pathways were investigated. The results demonstrated that a stable H2 production was reached after 3–4 days of operation. H2 production rates increased significantly with decreasing HRTv from 4 to 2 h. Instead, H2 yields remained almost stable despite the change in HRTv, indicating that the decrease in HRTv did not affect the global metabolism

Experimental strategy for hydrogen production from wastewater

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