High-Energy Molecular-Frame Photoelectron Angular Distributions: A Molecular Bond-Length Ruler

We present an experimental and theoretical study of core-level ionization of small hetero- and homo-nuclear molecules employing circularly polarized light and address molecular-frame photoelectron angular distributions in the light's polarization plane (CP-MFPADs). We find that the main forward-scattering peaks of CP-MFPADs are slightly tilted with respect to the molecular axis. We show that this tilt angle can be directly connected to the molecular bond length by a simple, universal formula. The extraction of the bond length becomes more accurate as the photoelectron energy is increased. We apply the derived formula to several examples of CP-MFPADs of C 1s and O 1s photoelectrons of CO, which have been measured experimentally or obtained by means of ab initio modeling. The photoelectron kinetic energies range from 70 to 1000~eV and the extracted bond lengths agree well with the known bond length of the CO molecule in its ground state. In addition, we discuss the influence of the back-scattering contribution that is superimposed over the analyzed forward-scattering peak in case of homo-nuclear diatomic molecules as N$_2$

Distribution and N2‐fixing activity of Frankia strains in relation to soil depth

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In Situ Transfer of Antibiotic Resistance Genes from Transgenic (Transplastomic) Tobacco Plants to Bacteria

Interkingdom gene transfer is limited by a combination of physical, biological, and genetic barriers. The results of greenhouse experiments involving transplastomic plants (genetically engineered chloroplast genomes) cocolonized by pathogenic and opportunistic soil bacteria demonstrated that these barriers could be eliminated. The Acinetobacter sp. strain BD413, which is outfitted with homologous sequences to chloroplastic genes, coinfected a transplastomic tobacco plant with Ralstonia solanacearum and was transformed by the plant's transgene (aadA) containing resistance to spectinomycin and streptomycin. However, no transformants were observed when the homologous sequences were omitted from the Acinetobacter sp. strain. Detectable gene transfer from these transgenic plants to bacteria were dependent on gene copy number, bacterial competence, and the presence of homologous sequences. Our data suggest that by selecting plant transgene sequences that are nonhomologous to bacterial sequences, plant biotechnologists could restore the genetic barrier to transgene transfer to bacteria

Rhizobium alamii improves water stress tolerance in a non-legume

International audienceWith the increasing demand for alternative solutions to replace or optimize the use of synthetic fertilizers and pesticides, the inoculation of bacteria that can contribute to the growth and health of plants (PGPR) is essential. The properties classically sought in PGPR are the production of phytohormones and other growth-promoting molecules, and more rarely the production of exopolysaccharides. We compared the effect of two strains of exopolysaccharide-producing Rhizobium alamii on rapeseed grown in a calcareous silty-clay soil under water stress conditions or not. The effect of factors ‘water stress’ and ‘inoculation’ were evaluated on plant growth parameters and the diversity of microbiota associated to root and root-adhering soil compartments. Water stress resulted in a significant decrease in leaf area, shoot biomass and RAS/RT ratio (root-adhering soil/root tissues), as well as overall beta-diversity. Inoculation with R. alamii YAS34 and GBV030 under water-stress conditions produced the same shoot dry biomass compared to uninoculated treatment in absence of water stress, and both strains increased shoot biomass under water-stressed conditions (+7% and +15%, respectively). Only R. alamii GBV030 significantly increased shoot biomass under unstressed or water-stressed conditions compared to the non-inoculated control (+39% and +15%, respectively). Alpha-diversity of the root-associated microbiota after inoculation with R. alamii YAS34 was significantly reduced. Beta-diversity was significantly modified after inoculation with R. alamii GBV030 under unstressed conditions. LEfSe analysis identified characteristic bacterial families, Flavobacteriaceae and Comamonadaceae, in the RT and RAS compartments for the treatment inoculated by R. alamii GBV030 under unstressed conditions, as well as Halomonadaceae (RT) and several species belonging to Actinomycetales (RAS). We showed that R. alamii GBV030 had a PGPR effect on rapeseed growth, increasing its tolerance to water stress, probably involving its capacity to produce exopolysaccharides, and other plant growth-promoting (PGP) traits

Type I Polyketide Synthases May Have Evolved Through Horizontal Gene Transfer

International audienceAbstract. Type I polyketide synthases (PKSI) are modular multidomain enzymes involved in the biosynthesis of many natural products of industrial interest. PKSI modules are minimally organized in three domains: ketosynthase (KS), acyltransferase (AT), and acyl carrier protein. The KS domain phylogeny of 23 PKSI clusters was determined. The results obtained suggest that many horizontal transfers of PKSI genes have occurred between actinomycetales species. Such gene transfers may explain the homogeneity and the robustness of the actinomycetales group since gene transfers between closely related species could mimic patterns generated by vertical inheritance. We suggest that the linearity and instability of actinomycetales chromosomes associated with their large quantity of genetic mobile elements have favored such horizontal gene transfers

High molecular weight DNA recovery from soils prerequisite for biotechnological metagenomic library construction

International audienceSoil is a complex environment considered as one of the main reservoirs of microbial diversity. However, the inability to cultivate most soil bacteria hampered fundamental attempts to determine the diversity of the prokaryotic world and limited its industrial exploitation. In the last 20 years, new methods have been developed to overcome these limitations based on the direct extraction of DNA from bacteria in their natural environment. In addition to fundamental research, the cloning of the extracted DNA for the development of metagenomic DNA clone libraries offers possibilities to discover novel bio-molecules through the expression of genes from uncultivated bacteria in surrogate bacterial hosts. However, such objectives require adapting DNA extraction methods and cloning strategies in order that entire gene clusters encoding biosynthetic pathway for secondary metabolites can be cloned. In this paper, we report that the size of DNA fragments extracted from soil varied in a range between less than 100 kb and more than 400 kb depending on the soil. The relatively limited size of DNA fragments extracted from some soil was not only due to mechanical, chemical or enzymatic shearing of the DNA during the extraction process but partly to the microbial growth status. Stimulating bacteria in situ by providing nutrients to the soil improved the size of extracted DNA, but it modified the bacterial community structure

Analyse et exploitation de la diversité génétique des polykétides synthases de type I dans l'ADN metagénomique d'un sol

National audienc

A possible role for phenyl acetic acid (PAA) on Alnus glutinosa nodulation by Frankia

International audienc