Paralyzing Action from a Distance in an Arboreal African Ant Species

Due to their prowess in interspecific competition and ability to catch a wide range of arthropod prey (mostly termites with which they are engaged in an evolutionary arms race), ants are recognized as a good model for studying the chemicals involved in defensive and predatory behaviors. Ants' wide diversity of nesting habits and relationships with plants and prey types implies that these chemicals are also very diverse. Using the African myrmicine ant Crematogaster striatula as our focal species, we adopted a three-pronged research approach. We studied the aggressive and predatory behaviors of the ant workers, conducted bioassays on the effect of their Dufour gland contents on termites, and analyzed these contents. (1) The workers defend themselves or eliminate termites by orienting their abdominal tip toward the opponent, stinger protruded. The chemicals emitted, apparently volatile, trigger the recruitment of nestmates situated in the vicinity and act without the stinger having to come into direct contact with the opponent. Whereas alien ants competing with C. striatula for sugary food sources are repelled by this behavior and retreat further and further away, termites defend their nest whatever the danger. They face down C. striatula workers and end up by rolling onto their backs, their legs batting the air. (2) The bioassays showed that the toxicity of the Dufour gland contents acts in a time-dependent manner, leading to the irreversible paralysis, and, ultimately, death of the termites. (3) Gas chromatography-mass spectrometry analyses showed that the Dufour gland contains a mixture of mono- or polyunsaturated long-chain derivatives, bearing functional groups like oxo-alcohols or oxo-acetates. Electrospray ionization-mass spectrometry showed the presence of a molecule of 1584 Da that might be a large, acetylated alkaloid capable of splitting into smaller molecules that could be responsible for the final degree of venom toxicity

A Secreted NlpC/P60 Endopeptidase from Photobacterium damselae subsp. piscicida Cleaves the Peptidoglycan of Potentially Competing Bacteria

Peptidoglycan (PG) is a major component of the bacterial cell wall, forming a mesh-like structure enwrapping the bacteria that is essential for maintaining structural integrity and providing support for anchoring other components of the cell envelope. PG biogenesis is highly dynamic and requires multiple enzymes, including several hydrolases that cleave glycosidic or amide bonds in the PG. This work describes the structural and functional characterization of an NlpC/P60-contain-ing peptidase from Photobacterium damselae subsp. piscicida (Phdp), a Gram-negative bacterium that causes high mortality of warm-water marine fish with great impact for the aquaculture industry. PnpA (Photobacterium NlpC-like protein A) has a four-domain structure with a hydrophobic and narrow access to the catalytic center and specificity for the γ-D-glutamyl-meso-diaminopimelic acid bond. However, PnpA does not cleave the PG of Phdp or PG of several Gram-negative and Gram-positive bacterial species. Interestingly, it is secreted by the Phdp type II secretion system and degrades the PG of Vibrio anguillarum and Vibrio vulnificus. This suggests that PnpA is used by Phdp to gain an advantage over bacteria that compete for the same resources or to obtain nutrients in nutrient-scarce environments. Comparison of the muropeptide composition of PG susceptible and resistant to the catalytic activity of PnpA showed that the global content of muropeptides is similar, suggesting that susceptibility to PnpA is determined by the three-dimensional organization of the muropeptides in the PG. IMPORTANCE Peptidoglycan (PG) is a major component of the bacterial cell wall formed by long chains of two alternating sugars interconnected by short peptides, generating a mesh-like structure that enwraps the bacterial cell. Although PG provides structural integrity and support for anchoring other components of the cell envelope, it is constantly being remodeled through the action of specific enzymes that cleave or join its components. Here, it is shown that Photobacterium damselae subsp. piscicida, a bacterium that causes high mortality in warm-water marine fish, produces PnpA, an enzyme that is secreted into the environment and is able to cleave the PG of potentially competing bacteria, either to gain a competitive advantage and/or to obtain nutrients. The specificity of PnpA for the PG of some bacteria and its inability to cleave others may be explained by differences in the structure of the PG mesh and not by different muropeptide composition.Europeu de Desenvolvimento Regional (FEDER) funds through the COMPETE 2020 Operacional Program for Competitiveness and Internationalization (POCI), Portugal 2020, and by Portuguese funds through Fundação para a Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior and Fundação para a Ciência e a Tecnologia (FCT), I.P., within the scope of the Norma Transitória - DL57/2016/CP1355/CT0010. This work had also support from the State Agency for Research (AEI) of Spain cofunded by the FEDER Program from the European Union (grants AGL2016-79738-R and BIO2016-77639-P

Study of exotic ants venoms : identification and characterization of an antimicrobial peptide

Les venins animaux, par leur richesse biochimique et la diversité de leurs cibles moléculaires, sont une source importante de molécules dont les applications potentielles sont nombreuses. La recherche de nouveaux médicaments pour remplacer certains antibiotiques devenus inefficaces face à l'apparition de résistances, est un axe fort de la recherche pharmacologique. Depuis plus de 40 ans, la découverte de toxines animales montre que les animaux venimeux peuvent être les « pharmaciens du futur ». Le venin de fourmis est encore peu étudié. Seul celui de quelques espèces a été exploré, avec à chaque fois la mise en évidence de toxines originales. L'objectif de cette thèse a été l'étude du venin de fourmis exotiques sur la base d'une approche pluridisciplinaire qui combine l'analyse biochimique et la toxinologie. Les travaux se sont articulés autour de deux axes principaux : (1) Recherche d'activités biologiques sur insectes et bactéries ; (2) Fractionnement des venins par des techniques séparatives et analyse biochimique des peptides isolés par spectrométrie de masse. Deux espèces de fourmis ont été choisies en fonction de leur mode de vie : Crematogaster striatula, une espèce arboricole et Tetramorium bicarinatum, une espèce terricole. Les différentes activités biologiques de leurs sécrétions venimeuses ont été conduites par test MTT. Le liquide de Dufour de C. striatula en plus de sa capacité à éloigner les espèces concurrentes montre une capacité à paralyser les termites de manière irréversible. Concernant le venin de T. bicarinatum, deux peptides ont été isolés et identifiés par spectrométrie de masse. La bicarinaline, peptide de 20 acides aminés et amidé à son extrémité C-terminale, s'est démarqué par son action antibactérienne à large spectre. Testée sur deux souches de staphylocoques, ce peptide se révèle aussi efficace voire plus puissant que la méllitine, peptide antimicrobien du venin d'abeille. La bicarinaline apparaît comme un candidat potentiel pour la conception de nouveaux traitements antibiotiques.Animal venoms, by their biochemical richness and diversity of molecular targets, are a highly significant source of new molecules, with numerous potential applications. A major thrust of present pharmacological research now concerns drugs to replace certain antibiotics, proven ineffective due to the appearance of resistant strains. And discoveries of animal toxins over the past 40 years or more, have shown that venomous species could be the « pharmacists of the future », with only a few species of ants' venoms having been studied, but each time resulting in the description of original toxins. The aim of this thesis has been to study the venom of tropical ants using a multidisciplinary approach combining biochemical analysis and toxinology, centred on two main areas: (1) Research into their biological activity on insects and bacteria; (2) Fractionation of venoms using separative techniques, plus biochemical analysis of the peptides isolated using mass spectrometry. Two species of ant have been chosen based on their lifestyles: Crematogaster striatula is arboricolous and Tetramorium bicarinatum, terricolous, and the different biological activities of their crude venoms have been investigated using the MTT test. The Dufour liquid of C. striatula, in addition to its ability to scare away competitors, can definitively paralyse termites. For the venom of T. bicarinatum, two peptides have been isolated, and identified using mass spectrometry. Bicarinalin, a short 20 amino acid residues C-terminally amidated peptide, was notable for its wide spectrum antibacterial activity which, when tested on two Staphylococcus strains, proved to be at least if not more potent than mellitin, the antimicrobial peptide from bee venom. Bicarinalin would thus appear to be a good candidate for the development of new antibiotic drugs

Etude toxinologique du venin de fourmis exotiques (identification et caractérisation d'un peptide antimicrobien)

Les venins animaux, par leur richesse biochimique et la diversité de leurs cibles moléculaires, sont une source importante de molécules dont les applications potentielles sont nombreuses. La recherche de nouveaux médicaments pour remplacer certains antibiotiques devenus inefficaces face à l'apparition de résistances, est un axe fort de la recherche pharmacologique. Depuis plus de 40 ans, la découverte de toxines animales montre que les animaux venimeux peuvent être les pharmaciens du futur . Le venin de fourmis est encore peu étudié. Seul celui de quelques espèces a été exploré, avec à chaque fois la mise en évidence de toxines originales. L'objectif de cette thèse a été l'étude du venin de fourmis exotiques sur la base d'une approche pluridisciplinaire qui combine l'analyse biochimique et la toxinologie. Les travaux se sont articulés autour de deux axes principaux : (1) Recherche d'activités biologiques sur insectes et bactéries; (2) Fractionnement des venins par des techniques séparatives et analyse biochimique des peptides isolés par spectrométrie de masse. Deux espèces de fourmis ont été choisies en fonction de leur mode de vie: Crematogaster striatula, une espèce arboricole et Tetramorium bicarinatum, une espèce terricole. Les différentes activités biologiques de leurs sécrétions venimeuses ont été conduites par test MTT. Le liquide de Dufour de C. striatula en plus de sa capacité à éloigner les espèces concurrentes montre une capacité à paralyser les termites de manière irréversible. Concernant le venin de T. bicarinatum, deux peptides ont été isolés et identifiés par spectrométrie de masse. La bicarinaline, peptide de 20 acides aminés et amidé à son extrémité C-terminale, s'est démarqué par son action antibactérienne à large spectre. Testée sur deux souches de staphylocoques, ce peptide se révèle aussi efficace voire plus puissant que la méllitine, peptide antimicrobien du venin d'abeille. La bicarinaline apparaît comme un candidat potentiel pour la conception de nouveaux traitements antibiotiques.Animal venoms, by their biochemical richness and diversity of molecular targets, are a highly significant source of new molecules, with numerous potential applications. A major thrust of present pharmacological research now concerns drugs to replace certain antibiotics, proven ineffective due to the appearance of resistant strains. And discoveries of animal toxins over the past 40 years or more, have shown that venomous species could be the pharmacists of the future , with only a few species of ants' venoms having been studied, but each time resulting in the description of original toxins. The aim of this thesis has been to study the venom of tropical ants using a multidisciplinary approach combining biochemical analysis and toxinology, centred on two main areas: (1) Research into their biological activity on insects and bacteria; (2) Fractionation of venoms using separative techniques, plus biochemical analysis of the peptides isolated using mass spectrometry. Two species of ant have been chosen based on their lifestyles: Crematogaster striatula is arboricolous and Tetramorium bicarinatum, terricolous, and the different biological activities of their crude venoms have been investigated using the MTT test. The Dufour liquid of C. striatula, in addition to its ability to scare away competitors, can definitively paralyse termites. For the venom of T. bicarinatum, two peptides have been isolated, and identified using mass spectrometry. Bicarinalin, a short 20 amino acid residues C-terminally amidated peptide, was notable for its wide spectrum antibacterial activity which, when tested on two Staphylococcus strains, proved to be at least if not more potent than mellitin, the antimicrobial peptide from bee venom. Bicarinalin would thus appear to be a good candidate for the development of new antibiotic drugs.MONTPELLIER-BU Pharmacie (341722105) / SudocSudocFranceF

Mycolactone Purification from M. ulcerans Cultures and HPLC-Based Approaches for Mycolactone Quantification in Biological Samples

International audienceMycolactones are a family of polyketide synthase products made by the human pathogen Mycobacterium ulcerans that were recently identified as novel inhibitors of the host membrane translocation complex (Sec61). Here, we provide protocols for the purification of mycolactones from bacterial cultures, and for their quantitative assessment in biological samples

Élargissement de la fenêtre de détection du zolpidem par la recherche de ses métabolites urinaires dans le cadre de la soumission chimique

Objectif : Dans le cadre de la soumission chimique, une méthode UPLC-MS/MS a été développée pour détecter le zolpidem et ses métabolites dans les urines. Méthodes : Pour déterminer les fenêtres de détection du zolpidem et de ses métabolites dans les urines, un volontaire a pris un comprimé de 10 mg. Les urines ont ensuite été collectées 30 min et 1 h après l'administration puis toutes les 12 h pendant 144 h. Après extraction sur cartouches Oasis$^{\circledR}$ MCX (SPE), les urines ont été analysées sur une colonne ACQUITY UPLCTM BEH C18, 1,7 μm ($2,1 \times 100$ mm) avec un gradient d'acide formique 0,1 % et d'acétonitrile, la détection a été effectuée au moyen d'un spectromètre de masse en tandem en utilisant deux transitions par composé. Résultats : Le zolpidem est détecté pendant 60 h, avec un pic après 12 h. Le métabolite I (acide 4-[(3-diméthylcarboylméthyl-6-méthyl)-imidazo-[1,2a]pyridine-2-yl]-benzoïque) est détecté jusqu'au dernier temps de la cinétique, tandis que le métabolite II (acide 3-diméthylcarbamoylméthyl-2-(4-méthylphényl)-imidazo-[1,2a]-pyridine-6-carboxylique) est détecté jusque 84 h après l'administration. Conclusion : Ainsi, dans le cas de soumission chimique impliquant le zolpidem, dans les urines le métabolite I apparaît être le meilleur marqueur pour caractériser une exposition

Altered spore cortex impairs virulence in <i>C. difficile</i>

International audienceSpores are produced by many organisms as the result of a survival mechanism, triggered under several types of adverse environmental conditions. They are multi-layered structures, composed of a compressed dehydrated inner core, surrounded by the inner membrane, a germ cell-wall, a peptidoglycan layer known as the cortex, an outer membrane, a proteinaceous external coat, and for some species the outermost layer called the exosporium. This study focuses on the spore cortex of Clostridium difficile, a Gram-positive spore-forming, toxin-producing anaerobic bacterium that can colonize the intestinal tracts of humans, considered as the leading cause of hospital and community-acquired antibiotic-associated diarrhea. Given the highly original structure described for the vegetative cell peptidoglycan of C. difficile, and notably the particularly high level of N-deacetylation and its impact on host-pathogen interactions, we focused on the cortex N-deacetylases, and especially the N-deacetylase responsible for muramic lactam synthesis in C. difficile. Moreover, given the central role of spores in the physiopathology of C. difficile infection, we also investigated the contribution of cortex structure in C. difficile virulence, presenting the first study connecting cortex structure and virulence. In this context, we provide the fine structure of C. difficile cortex and the characterization of pdaA as the N-deacetylase responsible for muramic lactams synthesis

Peptidoglycan analysis reveals that synergistic deacetylase activity in vegetative Clostridium difficile impacts the host response

International audienceClostridium difficile is an anaerobic and spore-forming bacterium responsible for 15-25% of postantibiotic diarrhea and 95% of pseudomembranous colitis. Peptidoglycan is a crucial element of the bacterial cell wall that is exposed to the host, making it an important target for the innate immune system. The C. difficile peptidoglycan is largely N-deacetylated on its glucosamine (93% of muropeptides) through the activity of enzymes known as N-deacetylases, and this N-deacetylation modulates host-pathogen interactions, such as resistance to the bacteriolytic activity of lysozyme, virulence, and host innate immune responses. C. difficile genome analysis showed that 12 genes potentially encode N-deacetylases; however, which of these N-deacetylases are involved in peptidoglycan N-deacetylation remains unknown. Here, we report the enzymes responsible for peptidoglycan N-deacetylation and their respective regulation. Through peptidoglycan analysis of several mutants, we found that the N-deacetylases PdaV and PgdA act in synergy. Together they are responsible for the high level of peptidoglycan N-deacetylation in C. difficile and the consequent resistance to lysozyme. We also characterized a third enzyme, PgdB, as a glucosamine N-deacetylase. However, its impact on N-deacetylation and lysozyme resistance is limited, and its physiological role remains to be dissected. Finally, given the influence of peptidoglycan N-deacetylation on host defense against pathogens, we investigated the virulence and colonization ability of the mutants. Unlike what has been shown in other pathogenic bacteria, a lack of N-deacetylation in C. difficile is not linked to a decrease in virulence

Muramic-δ-lactams are involved in <i>C. difficile</i> sporulation, germination and virulence

Background and aimsSpores are produced by many organisms as the result of a survival mechanism, triggered under several environmental conditions. They are multi-layered structures, one of which is a peptidoglycan layer known as the cortex. The cortex peptidoglycan has been described for several organisms, including B. subtilis and C. perfringens, but has yet to be published for C. difficile. Compared to the vegetative cell peptidoglycan, the cortex peptidoglycan possesses a unique, modified sugar called muramic-δ-lactam, synthesized by at least two enzymes: an amidase CwlD and an N-deacetylase PdaA. In this work, we analyzed the C. difficile cortex structure, we characterized the N-deacetylase involved in muramic-δ-lactam synthesis and investigated the impact of muramic-δ-lactams on C. difficile physiology and virulence.MethodsThe cortex of C. difficile 630∆erm and pdaA mutant strains were analyzed using UHPLC coupled HRMS. Germination was assessed through optical density monitoring of spore suspensions after addition of taurocholate. Spore resistance properties were investigated by enumeration of spore suspensions after treatment with ethanol, hydrogen peroxide or heat. Sporulation was studied in liquid cultures after 72H of growth. Morphology of both strains was assessed through transmission electron microscopy. ResultsThe cortex analysis revealed several differences between the B. subtilis and C. difficile cortex structures. For instance, only 24% of muropeptides in C. difficile carried muramic-δ-lactams, compared to 50% of muropeptides in B. subtilis. Analysis of the cortex from the pdaA mutant showed minor traces of muramic-δ-lactams (0.4% of all muropeptides). Investigation of the consequences of this decrease in muramic-δ-lactams in the pdaA mutant showed a decreased sporulation rate, an altered germination, and a decreased heat-resistance. In a virulence assay, the pdaA mutant also showed a delayed virulence.ConclusionsSurprisingly, our results suggest a much broader impact for muramic-δ-lactams in C. difficile compared to previously characterized model organisms, such as B. subtilis. Our results highlight a novel factor linking both the germination and sporulation processes, and provide an insight into a new strategy to target C. difficile and its dissemination by targeting enzymes involved in cortex synthesis