Saline Environments as a Source of Potential Quorum Sensing Disruptors to Control Bacterial Infections: A Review

Saline environments, such as marine and hypersaline habitats, are widely distributed around the world. They include sea waters, saline lakes, solar salterns, or hypersaline soils. The bacteria that live in these habitats produce and develop unique bioactive molecules and physiological pathways to cope with the stress conditions generated by these environments. They have been described to produce compounds with properties that differ from those found in non-saline habitats. In the last decades, the ability to disrupt quorum-sensing (QS) intercellular communication systems has been identified in many marine organisms, including bacteria. The two main mechanisms of QS interference, i.e., quorum sensing inhibition (QSI) and quorum quenching (QQ), appear to be a more frequent phenomenon in marine aquatic environments than in soils. However, data concerning bacteria from hypersaline habitats is scarce. Salt-tolerant QSI compounds and QQ enzymes may be of interest to interfere with QS-regulated bacterial functions, including virulence, in sectors such as aquaculture or agriculture where salinity is a serious environmental issue. This review provides a global overview of the main works related to QS interruption in saline environments as well as the derived biotechnological applications

Insight in the quorum sensing-driven lifestyle of the non-pathogenic Agrobacterium tumefaciens 6N2 and the interactions with the yeast Meyerozyma guilliermondii

Agrobacterium tumefaciens is considered a prominent phytopathogen, though most isolates are nonpathogenic. Agrobacteria can inhabit plant tissues interacting with other microorganisms. Yeasts are likewise part of these communities. We analyzed the quorum sensing (QS) systems of A. tumefaciens strain 6N2, and its relevance for the interaction with the yeast Meyerozyma guilliermondii, both sugarcane endophytes. We show that strain 6N2 is nonpathogenic, produces OHC8-HSL, OHC10-HSL, OC12-HSL and OHC12-HSL as QS signals, and possesses a complex QS architecture, with one truncated, two complete systems, and three additional QS-signal receptors. A proteomic approach showed differences in QS-regulated proteins between pure (64 proteins) and dual (33 proteins) cultures. Seven proteins were consistently regulated by quorum sensing in pure and dual cultures. M. guilliermondii proteins influenced by QS activity were also evaluated. Several up- and down- regulated proteins differed depending on the bacterial QS. These results show the importance of the QS regulation in the bacteria-yeast interactions.Fil: Bertini, Elisa Violeta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Torres, Mariela Analía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Leger, Thibaut. Institut Jacues Monod; FranciaFil: Garcia, Camille. Institut Jacques Monod; FranciaFil: KarWai, Hong. University Of Malaya; MalasiaFil: Teik Min, Chong. University Of Malaya; MalasiaFil: Castellanos, Lucia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: KokGan, Chan. University Of Malaya; MalasiaFil: Dessaux, Yves. Universite Paris-sud; FranciaFil: Camadro, Jean Michel. Institut Jacques Monod; FranciaFil: Nieto Peñalver, Carlos Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentin

Azospirillum Genomes Reveal Transition of Bacteria from Aquatic to Terrestrial Environments

Fossil records indicate that life appeared in marine environments ∼3.5 billion years ago (Gyr) and transitioned to terrestrial ecosystems nearly 2.5 Gyr. Sequence analysis suggests that “hydrobacteria” and “terrabacteria” might have diverged as early as 3 Gyr. Bacteria of the genus Azospirillum are associated with roots of terrestrial plants; however, virtually all their close relatives are aquatic. We obtained genome sequences of two Azospirillum species and analyzed their gene origins. While most Azospirillum house-keeping genes have orthologs in its close aquatic relatives, this lineage has obtained nearly half of its genome from terrestrial organisms. The majority of genes encoding functions critical for association with plants are among horizontally transferred genes. Our results show that transition of some aquatic bacteria to terrestrial habitats occurred much later than the suggested initial divergence of hydro- and terrabacterial clades. The birth of the genus Azospirillum approximately coincided with the emergence of vascular plants on land

6. OGM et agriculture

Inclure la question des OGM végétaux (organismes génétiquement modifiés) dans un ouvrage sur le développement durable est incontournable. En effet, dans le monde, à ce jour, plus de 160 millions d’hectares – soit environ 10 % des terres cultivables effectivement cultivées – sont dédiés aux variétés transgéniques*, et 50 % des productions de coton, maïs, soja et colza sont issues de telles lignées. Cependant, divers types d’OGM existent, et il est donc nécessaire d’expliquer ce que sont ces vé..

Collective expert scientific studies on “herbicide-tolerant varieties” : feedback from experience

These collective expert scientific studies on “herbicide-tolerant varieties” involved some twenty experts from very different disciplines in a “sensitive” topic. This article describes how the experts were chosen, how they interacted with their ministerial clients, how the group of experts functioned and the outcomes of its assessments. It investigates the way minority opinions were handled by the expert group, as well as the crucial question of recognition of the work of the scientists who took part, in relation to expectations among the research organisations.L’expertise scientifique collective « variétés tolérantes aux herbicides » a mobilisé une vingtaine d’experts de disciplines très différentes autour d’un sujet « sensible ». L’article décrit la façon dont ces experts ont été choisis, les modes d’interaction avec les commanditaires ministériels de l’expertise, le fonctionnement du collectif d’experts, ainsi que les « rendus » de l’expertise. Cet article aborde la question du traitement des avis minoritaires au sein du collectif et pose également la question centrale de la valorisation pour les scientifiques participant du travail fourni en lien avec les attentes des organismes de recherche

3. Colloque Rhizosphère : programme et résumés des communications

National audienc

Dégradation des N-acyl homosérine lactones, médiateurs de la régulation quorum sensing (les organismes, les mécanismes, les applications potentielles)

Les souches bactériennes d'une rhizosphere de tabac appartenant aux genres Comamonas, Pseudomonas, Rhodococcus et Variovorax présentent des cinétiques et des spectres de dégradation de N-AHSL variables. Parmi celles-ci, les souches de Comamonas sp. (D1) et de Rhodococcus (W2) sont capables d'inactiver toutes les N-AHSL quelques soient leurs substitutions sur le carbone 3. Ces deux souches sont capables d'interférer efficacement avec des fonctions régulées par QS chez d'autres bactéries. La dégradation des N-AHSL par la souche W2 est due à au moins deux activités enzymatiques : une activité oxydoréductase qui et une activité amidohydrolase, qui clive la liaison amide des N-AHSL, libérant de l'homosérine lactone et un acide gras. La première activité est non spécifique des N-AHSL puisque des analogues modifiés au niveau de leur chaîne latérale ou dépourvus du noyau lactone sont aussi réduits. La dégradation des N-AHSL par la souche D1 est aussi due à une activité amidohydrolase. Le criblage d'une banque d'ADN génomique de la souche W2 de Rhodococcus erythropolis a permis d'isoler un gène (qsdA) déterminant une activité " N-AHSLase ". Ce gène confère l'aptitude à dégrader les N-AHSL endogènes et exogènes à ses hôtes hétérologues. Il détermine une protéine présentant de fortes homologies avec les protéines de la famille des métallohydrolases : les phosphotriestérases (PTE). Cette protéine ne possède pas d'activité phosphotriestérase. La souche W2 possède au moins une seconde activité N-AHSLase, puisqu'un mutant possède toujours la capacité de dégrader les N-AHSL. Le gène qsdA, et l'activité qu'il code, semblent limités au genre Rhodococcus.Various bacterial strains from a tobacco rhizosphere belonging to the Comamonas, Pseudomonas, Rhodococcus and Variovorax genera harbour variable N-AHSL degradation kinetics and spectra. Among them, the strains Comamonas sp. (D1) and Rhodococcus erythropolis (W2) were capable to interfere with various functions regulated by quorum sensing. Strains D1 and W2 are able to inactivate a large range of N-AHSL as observed by HPLC analysis. The Rhodococcus strain harbours two N-AHSLase activities: the first one is an oxidoreductase and an amidohydrolase. This activity appeared to be also able to reduce N-AHSL analogues lacking in lactone ring or with a modified acyl chain. Another amidohydrolase activity was detected in the strain Comamonas sp. D1. It appeared that sequence or activity homologies were not so efficient tools to find functional homologues of N-AHSLases. Screening of the genomic library of the Rhodococcus erythropolis strain W2 permitted us to isolate and characterize one gene encoding an N-AHSLase activity that termed qsdA. This gene presents a strong homology with members of the metalohydrolase super family: the phosphotriesterases (PTE). However, QsdA did not exhibit any phosphotriesterases activity and a strain with a PTE activity had no ability to degrade N-AHSL. In addition, strain W2 harbors a second N-AHSLase activity as a mutant harbouring a disrupted qsdA gene retains the ability to degrade N-AHSL. The qsdA gene and the relevant encoded activity are characteristic, so far, for the Rhodococcus genera. It may have evolved from PTE genes after the emergence of this genus in the bacterial evolution.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

The Development of HTV Cropping Systems

International audienceThe introduction of an HT crop into an existing cropping system is accompanied by changes in chemical weed control techniques, but also, either directly or indirectly, by changes in other agricultural practices at the field level. The first part of this chapter deals with the management of weed flora. The second part will seek to describe current trends in the evolution of French cropping systems, which constitute the context within which HTVs would be introduced

Mechanisms of Herbicide Resistance and HTV Breeding Techniques

International audienceIn this chapter, we will first consider the modes of action of the principal herbicides used with HTVs, and the mechanisms at work in plants and microorganisms showing resistance to these substances. Next we will describe the various techniques for introducing the HT trait into cultivated varieties (cultivars). Finally, we will present the principal HTV-herbicide pairs that have been obtained with these techniques up to the present time