Plateforme GenoSol : une structure logistique d'appui à la recherche sur la microbiologie des sols et de l'environnement

EA SPE GenoSol EcolDur CT3; Les communautés microbiennes du sol sont difficiles à caractériser. Ceci s’explique par une accessibilité plus ou moins importante des populations au sein d’une matrice hétérogène et structurée mais aussi par leur densité et diversité très importante qui rend difficile à résoudre l’information obtenue. Toutefois, grâce aux avancées méthodologiques qui ont eu lieu depuis une quinzaine d’années, les études d’écologie microbienne bénéficient maintenant d’une automatisation des outils moléculaires (extraction d’ADN, caractérisation du polymorphisme de l’ADN, séquençage haut débit, métagénomique, métaprotéomique…) permettant la caractérisation des ressources génétique…

Impact of inoculation with the phytostimulatory PGPR Azospirillum lipoferum CRT1 on the genetic structure of the rhizobacterial community of field-grown maize

International audience; The phytostimulatory PGPR Azospirillum lipoferum CRT1 was inoculated to maize seeds and the impact on the genetic structure of the rhizobacterial community in the field was determined during maize growth by Automated Ribosomal Intergenic Spacer Analysis (ARISA) of rhizosphere DNA extracts. ARISA fingerprints could differ from one plant to the next as well as from one sampling to the next. Inoculation with strain CRT1 enhanced plant-to-plant variability of the ARISA fingerprints and caused a statistically significant shift in the composition of the indigenous rhizobacterial community at the first two samplings. This is the first study on the ecological impact of Azosp…

Interaction between Medicago truncatula and Pseudomonas fluorescens: evaluation of costs and benefits across an elevated atmospheric CO2.

10 pages; International audience; Soil microorganisms play a key role in both plants nutrition and health. Their relation with plant varies from mutualism to parasitism, according to the balance of costs and benefits for the two partners of the interaction. These interactions involved the liberation of plant organic compounds via rhizodeposition. Modification of atmospheric CO2 concentration may affect rhizodeposition and as a consequence trophic interactions that bind plants and microorganisms. Positive effect of elevated CO2 on plants are rather well known but consequences for micoorganisms and their interactions with plants are still poorly understood. A gnotobiotic system has been devel…

Biologie des communautés dans la rhizosphère : analyse des interactions plantes - champignons mycorhizogènes à arbuscules - bactéries

National audience

Plant genotype: a lever in the interactions between plant and its associated rhizosphere microbiome

International audience; In the context of highly pressured agricultural production using low levels of inputs, cropping strategies could take advantage of existing plant-microbiome interactions that can improve both plant growth and health. We believe that plant genetics can provide some clues to better understand the mechanisms underlying microbiome recruitment by the plant.The aims of this work were (i) to assess plant genotype effect on the rhizosphere bacterial communities in relation to the plant nutritional strategies for a core collection of 155 genotypes of Medicago truncatula and (ii) to highlight the genetic determinisms potentially associated in these interactions. To achieve the…

Quel renouvellement des questions de recherches sur les légumineuses ?

Strategies for analyzing interactions between arbuscular mycorrhiza and bacteria

National audience

Molecular biomass and MetaTaxogenomic assessment of soil microbial communities as influenced by soil DNA extraction procedure

Three soil DNA extraction procedures (homemade protocols and commercial kit) varying in their practicability were applied to contrasting soils to evaluate their efficiency in recovering: (i) soil DNA and (ii) bacterial diversity estimated by 16S rDNA pyrosequencing. Significant differences in DNA yield were systematically observed between tested procedures. For certain soils, 10 times more DNA was recovered with one protocol than with the others. About 15,000 sequences of 16S rDNA were obtained for each sample which were clustered to draw rarefaction curves. These curves, as well as the PCA ordination of community composition based on OTU clustering, did not reveal any significant differenc…

Medicago species affect the community composition of arbuscular mycorrhizal fungi associated with roots

National audience; The symbiosis between plants and arbuscular mycorrhizal fungi (AMF) is ancient and involves 80% of terrestrial plant families. The symbiotic association between AMF and plants was described to be non specific. However, AMF were reported to influence plant community diversity and productivity. On the other way, the effect of plant genotypes belonging to closely related species on AMF diversity has not been explored so far. The aim of this work was to assess the impact of four different Medicago species, M. laciniata, M. murex, M. polymorpha and M. truncatula cv. Jemalong J5, on the composition of AM fungal community, when cultivated in a silty-thin clay soil (Mas d’Imbert,…

Diversité microbienne des sols : stratégie méthodologique, distribution spatiale et traduction en fonctionnement biologique

International audience; Since the development of industrialization, urbanization and agriculture, soils have been subjected to numerous variations in environmental conditions, which have resulted in modifications of the taxonomic diversity and functioning of the indigenous microbial communities. As a consequence, the functional significance of these losses/modifications of biodiversity, in terms of the capacity of ecosystems to maintain the functions and services on which humanity depends, is now of pivotal importance. In this context, one of the main challenges in soil microbial ecology is to better understand and predict the processes that drive soil microbial diversity and the link betwe…

Soil microbial diversity effects on primary production and symbiotic interactions

SPEEAEcolDurGenoSolGEAPSI; The importance of telluric microorganisms linked together by trophic exchanges with plants, that sustain all ecosystems through primary production, is known. However, the role of soil microbial diversity for primary production remains controversial. A diversity decreasing was achieved, by inoculating a sterilized soil with serial dilutions of a suspension from the same non-sterilized soil, to determine the consequences of microbial diversity erosion on the growth and fitness of three plant species more or less dependent on symbionts, Medicago truncatula, Brachypodium distachyon and Arabidopsis thaliana. The results showed that the impact of microbial diversity dec…

Characterization of Bacterial and Fungal Soil Communities by Automated Ribosomal Intergenic Spacer Analysis Fingerprints: Biological and Methodological Variability

ABSTRACT Automated rRNA intergenic spacer analysis (ARISA) was used to characterise bacterial (B-ARISA) and fungal (F-ARISA) communities from different soil types. The 16S-23S intergenic spacer region from the bacterial rRNA operon was amplified from total soil community DNA for B-ARISA. Similarly, the two internal transcribed spacers and the 5.8S rRNA gene (ITS1-5.8S-ITS2) from the fungal rRNA operon were amplified from total soil community DNA for F-ARISA. Universal fluorescence-labeled primers were used for the PCRs, and fragments of between 200 and 1,200 bp were resolved on denaturing polyacrylamide gels by use of an automated sequencer with laser detection. Methodological (DNA extracti…

Traduction de la métagenomique des agrosystemes en services écologiques

International audience; En affectant les communautés microbiennes présentes dans le sol, les pratiques agricoles mettent en péril la biodiversité des agrosystèmes. La génomique environnementale est un nouveau moyen d’améliorer nos connaissances sur ces derniers et ce faisant, de concevoir des systèmes agricoles plus respectueux de l’environnement.

Distribution and diversity of type III secretion system-like genes in saprophytic and phytopathogenic fluorescent pseudomonads

Type three secretion systems (TTSSs) are protein translocation mechanisms associated with bacterial pathogenicity in host plants, and hypersensitive reactions in non-host plants. Distribution and diversity of TTSS-like genes within a collection of saprophytic and phytopathogenic fluorescent pseudomonads were characterized. This collection included 16 strains belonging to 13 pathogenic species, and 87 strains belonging to five saprophytic species isolated from plant rhizosphere and soil. Presence of conserved hypersensitive reaction/pathogenicity (hrp) genes (hrc RST) was assessed both by PCR using primers designed to amplify the corresponding sequence and by dot-blot hybridization using a P…

Dynamic of the genetic structure of bacterial and fungal communities at different developmental stages of Medicago truncatula Gaertn. cv. Jemalong line J5

International audience; The genetic structure of bacterial and fungal communities was characterized in the rhizosphere of Medicago truncatula Gaertn. cv. Jemalong line J5 at five developmental stages (three vegetative and two reproductive stages), and in three compartments (bulk soil, rhizosphere soil and root tissues). The genetic structure of microbial communities was determined by cultivation-independent methods using directly extracted DNA that was characterized by automated ribosomal intergenic spacer analysis (ARISA). Principal component analyses (PCA) indicate that, for all developmental stages, the genetic structure of microbial communities differed significantly by compartment, wit…

Legumes in 21st century Europe: present and future importance in agri-food systems? New challenges for reseach.

Intensification of agriculture since 1950 has globally led to the decline of grain legume crops, which currently represent less than 3 % of arable crops in France and Europe. Nevertheless, legumes have several major assets (i) as plant proteins for animal feed and human food and (ii) as plants fixing atmospheric N2 and thereby saving nitrogen inputs in cropping systems, and (iii) as diversification crops. The analysis of forage and grain legume producing systems in France showed that the dominant system results in a lock-in of the different factors limiting legume insertion into the current systems. But legumes could have a major role to play in the agroecological transition towards more su…

Fluorescent pseudomonads harboring type III secretion genes are enriched in the mycorrhizosphere of Medicago truncatula

Type III secretion systems (T3SSs) of Gram-negative bacteria mediate direct interactions with eukaryotic cells. Pseudomonas spp. harboring T3SS genes (T3SS+) were previously shown to be more abundant in the rhizosphere than in bulk soil. To discriminate the contribution of roots and associated arbuscular mycorrhizal fungi (AMF) on the enrichment of T3SS+ fluorescent pseudomonads in the rhizosphere of Medicago truncatula, their frequency was assessed among pseudomonads isolated from mycorrhizal and nonmycorrhizal roots and from bulk soil. T3SS genes were identified by PCR targeting a conserved hrcRST DNA fragment. Polymorphism of hrcRST in T3SS+ isolates was assessed by PCR-restriction fragm…

Validation and application of a PCR primer set to quantify fungal communities in the soil environment by real-time quantitative PCR

Fungi constitute an important group in soil biological diversity and functioning. However, characterization and knowledge of fungal communities is hampered because few primer sets are available to quantify fungal abundance by real-time quantitative PCR (real-time Q-PCR). The aim in this study was to quantify fungal abundance in soils by incorporating, into a real-time Q-PCR using the SYBRGreen (R) method, a primer set already used to study the genetic structure of soil fungal communities. To satisfy the real-time Q-PCR requirements to enhance the accuracy and reproducibility of the detection technique, this study focused on the 18S rRNA gene conserved regions. These regions are little affec…

Microdiversity of Burkholderiales associated with mycorrhizal and nonmycorrhizal roots of Medicago truncatula

The genetic diversity of bacterial communities associated with mycorrhizal and nonmycorrhizal roots of Medicago truncatula was characterized by two approaches. Firstly, phylogenetic analysis was performed on 164 partial 16S rRNA gene-intergenic spacer (IGS) sequences from operational taxonomic units previously shown to be preferentially associated with mycorrhizal roots. These sequences were distributed into three branches corresponding to Comamonadaceae, Oxalobacteraceae and Rubrivivax subgroups. Most sequences were obtained from mycorrhizal roots, indicating the preferential association of the corresponding families with mycorrhizal roots. A second phylogenetic analysis was performed on t…

A new conceptual framework shows that plant genotype and soil nitrogen availability modify both plant nutritional strategies and diversity of their associated rhizosphere microbiome

In the context of sustainable agriculture, it is desirable to lower the input of mineral fertilizers. Therefore, we need to select ‘new’ genotypes that are both adapted to ‘low fertilizer inputs’ and more efficient in nutrient use. A better understanding of plant-microbe interactions under low input of fertilizers is now needed. Nevertheless, in microbial ecology, conceptual frameworks or models are used to analyse plant-microbe interactions but plant phenotype is currently viewed as a “black box”. We developed a new conceptual framework to study plant-microbe interactions using a multidisciplinary approach combining Microbial Ecology and Plant Ecophysiology.The links among plant genotype, …

Etude de l’interaction « Plante x Communauté microbienne du sol » chez l’espèce modèle Medicago truncatula

National audience

Diversité et activités microbiennes dans la rhizosphère: des atouts majeurs en agroécologie

National audience; Les rhizodépôts libérés par les plantes stimulent une microflore abondante et active dans la rhizosphère. La diversité des communautés microbiennes correspondantes est influencée par la nature des rhizodépôts (composition, molécules signal) qui diffère selon les génotypes végétaux. Le coût pour la plante correspondant à la libération de ces rhizodépôts est contrebalancé par le bénéfice issu des effets positifs de certaines populations microbiennes rhizosphériques sur la croissance et la santé de la plante-hôte. La connaissance des traits végétaux impliqués dans la sélection de ces populations bénéfiques, au sein des communautés microbiennes telluriques, représente un enje…

Optimisation du pyroséquençage haut-débit pour caractériser la diversité taxonomique des communautés bactériennes des sols

Affiche, résumé; International audience; La diversité microbienne d’un sol (que l’on estime entre 100 000 et 1 000 000 d’espèces différentes par gramme de sol) est difficile à caractériser. Toutefois, d’importantes avancées en biologie moléculaire, comme le développement du pyroséquençage, ont permis d'obtenir plusieurs centaines de milliers de séquences à partir d’un ADN méta-génomique. Ces nouveaux développements permettent maintenant de caractériser la diversité des communautés microbiennes du sol en se basant sur un marqueur phylogénétique comme l'ADNr 16S, aussi appelée MetaTaxogénomique (Maron et coll., 2011). Toutefois, dans un contexte ou l’écologie microbienne du sol commence à s’a…

Diversity of root-associated fluorescent pseudomonads as affected by ferritin overexpression in tobacco

A transgenic tobacco overexpressing ferritin (P6) was recently shown to accumulate more iron than the wild type (WT), leading to a reduced availability of iron in the rhizosphere and shifts in the pseudomonad community. The impact of the transgenic line on the community of fluorescent pseudomonads was assessed. The diversity of 635 isolates from rhizosphere soils, rhizoplane + root tissues, and root tissues of WT and P6, and that of 98 isolates from uncultivated soil was characterized. Their ability to grow under iron stress conditions was assessed by identifying their minimal inhibitory concentrations of 8-hydroxyquinoline for each isolate, pyoverdine diversity by isoelectrofocusing and ge…

Studying the arbuscular mycorrhizal symbiosis from axenic system to soilborne interactions by proteomics: which challenges to face?

Maîtrise et gestion de la biodiversité dans les sols: quelles perspectives ?

National audience

Apport des nouvelles générations de séquençage pour accéder à la diversité des communautés microbiennes du sol : nécessité d’un ‘pipeline’ bio-informatique pour les biologistes

Communication orale, résuméCommunication orale, résumé; La diversité microbienne d’un sol est difficile à caractériser. Ceci s’explique par une accessibilité plus ou moins importante des populations au sein d’une matrice hétérogène et structurée, mais aussi par l’incapacité à résoudre une information constituée de 100 000 à 1 000 000 d’espèces différentes par gramme de sol. Toutefois, récemment, d’importantes avancées en biologie moléculaire ont permis de mieux caractériser la diversité des communautés microbiennes du sol in situ et ce sans a priori. Ainsi, la puissance des nouvelles générations de séquençage comme le pyroséquençage permettent de travailler en haut-débit afin d’obtenir plus…

Crosstalks between soil microbial communities and a nitrogen fixing legume species (medicago truncatula) during its Vegetative Stage

International audience

egc, a hyfhly prevalent operon of enterotixin gene, forms a putative nursery of superantigens in Staphylococcus aureus

International audience

Biogeography of soil microbial communities: a review and a description of the ongoing french national initiative

International audience; Microbial biogeography is the study of the distribution of microbial diversity on large scales of space and time. This science aims at understanding biodiversity regulation and its link with ecosystem biological functioning, goods and services such as maintenance of productivity, of soil and atmospheric quality, and of soil health. Although the initial concept dates from the early 20th century (Beijerinck (1913) De infusies en de ontdekking der backterien, in: Jaarboek van de Knoniklijke Akademie van Wetenschappen, Muller, Amsterdam), only recently have an increasing number of studies have investigated the biogeographical patterns of soil microbial diversity. A such …

Effet de la rotation des cultures sur la microflore du sol et son activité

Quel renouvellement des questions de recherche sur les légumineuses ?

Conclusion du workshop; National audience

Iron dynamics in the rhizosphere as a case study for analysing interactions among soils, plants and microbes

International audience

Combining ecophysiological and microbial ecological approaches to assess interaction between genotypes of Medicago truncatula and the soil bacterial communities

International audience; Microbial communities can play a key role in sustainable agriculture by improving crop growth. Currently, a major stake is to study the effect of the plant genotype on the shaping of the soil microbial communities in relation to the plant nutrition. Methods: The links between the plant genotype and the rhizospheric bacterial communities were assessed at both structural and functional level using a multidisciplinary approach. On the one side, the genetic structure (Automated Ribosomial Intergenic Spacer Analysis (ARISA)) and diversity (454 pyrosequencing) of bacterial communities of the rhizosphere was first analysed. On the other side, using an ecophysiological model…

Dynamics and identification of soil microbial populations actively assimilating carbon from 13C-labelled wheat residue as estimated by DNA- and RNA-SIP techniques.

International audience; This work is the first report on the use of DNA-, RNA-SIP approaches to elucidate the dynamics and the diversity of bacterial populations actively assimilating C derived from plant residues labelled at more than 90% (13)C. Wheat-residues, were incorporated and incubated into soil microcosms for 28 days. At the end of the incubation time, no more than 55% of the total CO(2) released was (13)C-labelled, suggesting the occurrence of an important priming effect process. After 7 days, more than 30% of the whole DNA extracted were labelled, allowing an efficient separation of labelled from unlabelled DNA using density gradient centrifugation. The genetic structure of bacte…

Influence du système de sécrétion de type III bactérien dans les intéractions plantes-Pseudomonas spp. fluorescents non pathogènes

http://prodinra.inra.fr/record/271693SPEEAEcolDurCT3; L’objectif de cette thèse a été de contribuer à faire progresser les connaissances sur les interactions bénéfiques entre les plantes et les microorganismes en évaluant la contribution des systèmes de sécrétion de type III (SST3). Une synthèse des connaissances disponibles relatives aux SST3 chez les Pseudomonas non pathogènes, saprotrophes ou mutualistes, montre que les SST3 ne sont pas cantonnés aux interactions parasites ou pathogènes avec les plantes. Dans la première étude expérimentale, nous avons utilisé différents génotypes de Medicago truncatula Gaertn. cv. Jemalong capables (Myc+) ou non (Myc-) d’établir une symbiose mycorhizien…

Combining molecular microbial ecology with ecophysiology and plant genetics for a better understanding of plant-microbial communities' interactions in the rhizosphere.

18 pages; International audience

Apport des nouvelles générations de séquençage pour accéder à la diversité des communautés microbiennes du sol : nécessité d’un ‘pipeline’ bio-informatique pour les biologistes

National audience

Response of soil bacterial community structure to successive perturbations of different types and intensities

SummaryIn soil, genetic structure modifications of indigenousbacterial community consecutively to a severe stress(mercury contamination) were delayed when thecommunity was pre-exposed to various minor per-turbations (heat, copper and atrazine). Such minorperturbations induced transitory community struc-ture modifications leading to an increase of commu-nity stability towards a severe mercury stress. Theseresults illustrated well the short-term pre-adaptationprocess for bacterial community hypothesizing thatcommunity submitted to perturbations become moreresistant to withstand another stress. Compared with other environmental matrices of the bio-sphere, soils are considered as the main reservo…

Identification of bacterial groups preferentially associated with mycorrhizal roots of Medicago truncatula

ABSTRACT The genetic structures of bacterial communities associated with Medicago truncatula Gaertn. cv. Jemalong line J5 (Myc + Nod + ) and its symbiosis-defective mutants TRV48 (Myc + Nod − ) and TRV25 (Myc − Nod − ) were compared. Plants were cultivated in a fertile soil (Châteaurenard, France) and in soil from the Mediterranean basin showing a low fertility (Mas d'Imbert, France). Plant growth, root architecture, and the efficiency of root symbiosis of the three plant genotypes were characterized in the two soils. Structures of the bacterial communities were assessed by automated-ribosomal intergenic spacer analysis (A-RISA) fingerprinting from DNA extracted from the rhizosphere soil an…

Microbial metacommunity: a METABAR coding approach

Microbial metacommunity: a METABAR coding approach. 2017 Scientific MEM days: Journées scientifiques MEM (Métaomiques et écosystèmes microbiens)

Platform GenoSol: a new tool for conserving and exploring soil microbial diversity

International audience; Soils are the principal reservoirs of microbial diversity and represent a core component of terrestrial ecosystems. There is an increasing demand for assessing the impact of agricultural and industrial practices on the environment at large scales in a context of global change. To address this demand, taxonomic and functional diversity of soil microbial communities, and their stability over time need to be characterized for predicting soil quality upon human activities, the evolution of this quality being expected to affect environment quality and public health. Recent methodological progresses have led to the development and automation of molecular biological tools (…

Toward an integrated approach for studying plant-microbe interactions in the rhizosphere: from genomic to proteomic

International audience

Holobionte : concept et enjeux pour la biologie des plantes et la génétique

National audience

Microbial ecology of the rhizosphere

Part II. Selected MethodsPlant-microbe Chapitre 9 : Interactions and Soil Quality; International audience

Comparative genetic diversity of the narG, nosZ, and 16S rRNA genes in fluorescent Pseudomonads

ABSTRACT The diversity of the membrane-bound nitrate reductase ( narG ) and nitrous oxide reductase ( nosZ ) genes in fluorescent pseudomonads isolated from soil and rhizosphere environments was characterized together with that of the 16S rRNA gene by a PCR-restriction fragment length polymorphism assay. Fragments of 1,008 bp and 1,433 bp were amplified via PCR with primers specific for the narG and nosZ genes, respectively. The presence of the narG and nosZ genes in the bacterial strains was confirmed by hybridization of the genomic DNA and the PCR products with the corresponding probes. The ability of the strains to either reduce nitrate or totally dissimilate nitrogen was assessed. Overa…

Relationships between Staphylococcus aureus genetic background, virulence factors, agr groups (alleles), and human disease

ABSTRACT The expression of most Staphylococcus aureus virulence factors is controlled by the agr locus, which encodes a two-component signaling pathway whose activating ligand is an agr -encoded autoinducing peptide (AIP). A polymorphism in the amino acid sequence of the AIP and of its corresponding receptor divides S. aureus strains into four major groups. Within a given group, each strain produces a peptide that can activate the agr response in the other member strains, whereas the AIPs belonging to different groups are usually mutually inhibitory. We investigated a possible relationship between agr groups and human S. aureus disease by studying 198 S. aureus strains isolated from 14 asym…

Effect of ferritin overexpression in tobacco on the structure of bacterial and pseudomonad communities associated with the roots

The genetic structures of total bacterial and pseudomonad communities were characterized in rhizosphere soil and rhizoplane+root tissues of tobacco wild type and a ferritin overexpressor transgenic line (P6) by a cultivation-independent method using directly extracted DNA at the end of three consecutive plant cultures. The structure of total bacterial communities was characterized by automated ribosomal intergenic spacer analysis (A-RISA), and that of pseudomonad communities was characterized by PCR-restriction fragment length polymorphism (PCR-RFLP) from DNA amplified with specific primers. The structure of total bacterial communities was significantly modified in the rhizosphere soil by t…

Assessing genetic structure and diversity of airborne bacterial communities by DNA fingerprinting and 16S rDNA clone library

Abstract The density, genetic structure and diversity of airborne bacterial communities were assessed in the outdoor atmosphere. Two air samples were collected on the same location (north of France) at two dates (March 2003 (sample1) and May 2003 (sample 2)). Molecular culture-independent methods were used to characterise airborne bacterial communities regardless of the cell culturability. The automated-ribosomal intergenic spacer analysis (A-RISA) was performed to characterise the community structure in each sample. For both sampling dates, complex A-RISA patterns were observed suggesting a highly diverse community structure, comparable to those found in soil, water or sediment environment…

CHASE : an extracellular sensing domain common to transmembrane receptors from prokariotes, lower eukaryotes and plants

International audience

Costs-benfits trade-off in the intercation between Medicago truncatula and Pseudomonas fluorescens C7R12 across atmospheric carbon dioxide modulation

The interactions between plants and soil microorganisms are mainly based on trophic relationships. The compounds exchanged represent cost for the organism produces them but a benefit for the one who receive those compounds. A mutualistic relation leads to stability in the cost-benefit balance resulting from a co-evolution between the two organisms. The cost corresponding for the release of carbon compounds by the plant would be offset by benefits in return corresponding for the activities of microorganisms that use them. We tested by an experimental way the effect of CO2 concentration on the interaction between M. truncatula and the bacterium P. fluorescens C7R12. The results allowed a best…

Optimisation du pyroséquençage haut-débit pour caractériser la diversité taxonomique des communautés bactériennes des sols

La diversité microbienne d’un sol (que l’on estime à 100000 à 1000000 d’espè ces différentes par gramme de sol) est difficile à caractériser. Toutefois, d’importantes avancé es en biologie moléculaire (comme le développement du pyrosé quençage), ont permis d'obtenir plusieurs centaines de milliers de sé quences à partir d’un ADN métagénomique, permettant une meilleure caracté risation de la diversité des communautés microbiennes du sol. Toutefois, dans un contexte ou l’écologie microbienne du sol commence à s’accaparer les é chantillonnages de grande envergure (spatial et temporelle) afin de mieux hié rarchiser les processus et paramètres impliqués dans la diversification de ces communauté …

Direct conjugal transfers of Ti plasmid to soil microflora

The bacterial species in soil that can receive a Ti plasmid by conjugation from Agrobacterium spp. were investigated. In order to have direct access to the potential reservoir of Ti plasmid amongst soil microflora, the conjugal system consisting of a multiply auxotrophic derivative of C58 (ST-96-4) and a derivative of pTiC58Delta(acc)R (pSTiEGK) containing a triple antibiotic-resistance cassette in traM was used to transfer the Ti plasmid in a complex soil microflora used as the recipient. Numerous transconjugants were obtained by this method but none was identified as Agrobacterium. This could be explained by the low density of Agrobacterium in the tested soil. As indicated by analysis of …

Temporal variability of airborne bacterial community structure in an urban area

International audience; Temporal airborne bacterial genetic community structure and meteorological factors were analysed above an urban area in the northwest of France from December 2003 to April 2004 with a sampling strategy considering different time intervals (from an hour to a month). Principal component analysis (PCA) of B-ARISA (Bacterial-Automated Ribosomal Intergenic Spacer Analysis) profiles revealed a hierarchy in the temporal variability of bacterial community: daily<weekly<seasonal. Co-inertia analysis between B-ARISA data and meteorological factors demonstrated the correlation between the seasonal variability in the bacterial community and climatic conditions such as temperatur…

Proteomes of arbuscular mycorrhizal symbiosis : past and present achievements

Evidence of a core microbiota shaped by plant and earthworm interactions across soils

Prod 2018-139a EA AGROSUP INRA BIOME IPM; International audience; While having distinct niches, plants and earthworms have occupied soils over geological times, mutually influencing each-others. These macroorganisms are considered “ecosystem engineers”, actively modifying soil physical structure, which notably provides specific habitats for microorganisms: the rhizosphere and the drilosphere (casts/burrows produced by earthworms). In this study, we aimed to disentangle the relative importance of both macroorganisms in shaping microbial community assembly in different soil types, and determine the extent and modalities of how rhizosphere and drilosphere communities may coalesce with each-oth…

Effect of arbuscular mycorrhiza establishment on the genetic structure and diversity of bacteria in the rhizosphere of Medicago truncatula

National audience; The rhizosphere is the volume of soil which is influenced by plant root activity. Plant roots release 20% of the photosynthates into the rhizosphere. This process sustains the development of an active free living microflora in the rhizosphere compared to the bulk soil. Plants establish also symbiotic associations with soil microorganisms. Arbuscular mycorrhizas (AM) are mutualistic symbioses between soil fungi and plant roots. AM contribute to plant adaptation to low fertility environments. AM are established by 80% of terrestrial plant families including major crop plants. AM are also ancient symbiosis (400 million years). AM are known to be non-specific associations. Ho…

Interactions durables entre plantes et microorganismes dans les sols

National audience

Fingerprinting and diversity of bacterial copA genes in response to soil types, soil organic status and copper contamination

A molecular fingerprinting assay was developed to assess the diversity of copA genes, one of the genetic determinants involved in bacterial resistance to copper. Consensus primers of the copA genes were deduced from an alignment of sequences from proteobacterial strains. A PCR detection procedure was optimized for bacterial strains and allowed the description of a novel copA genetic determinant in Pseudomonas fluorescens. The copA DNA fingerprinting procedure was optimized for DNA directly extracted from soils differing in their physico-chemical characteristics and in their organic status (SOS). Particular copA genetic structures were obtained for each studied soil and a coinertia analysis …

Reciprocal interactions between plants and fluorescent pseudomonads in relation with iron in the rhizosphere

communication orale invitée; absent

Translation of metagenomics agroecosystems in ecological services

National audience

Contamination of soil by copper affects the dynamics, diversity, and activity of soil bacterial communities involved in wheat decomposition and carbon storage.

ABSTRACT A soil microcosm experiment was conducted to evaluate the influence of copper contamination on the dynamics and diversity of bacterial communities actively involved in wheat residue decomposition. In the presence of copper, a higher level of CO 2 release was observed, which did not arise from greater wheat decomposition but from a higher level of stimulation of soil organic matter mineralization (known as the priming effect). Such functional modifications may be related to significant modifications in the diversity of active bacterial populations characterized using the DNA stable-isotope probing approach.

Comment les bactéries perçoivent et répondent aux modifications de leur environnement ? Génomique comparative des systèmes à deux composantes bactériens : organisation, distribution et fonction

National audience

Sampling strategy in molecular microbial ecology: influence of soil sample size on DNA fingerprinting analysis of fungal and bacterial communities.

Assessing soil microbial community structure by the use of molecular techniques requires a satisfactory sampling strategy that takes into account the high microbial diversity and the heterogeneous distribution of microorganisms in the soil matrix. The influence of the sample size of three different soil types (sand, silt and clay soils) on the DNA yield and analysis of bacterial and fungal community structure were investigated. Six sample sizes from 0.125 g to 4 g were evaluated. The genetic community structure was assessed by automated ribosomal intergenic spacer analysis (A-RISA fingerprint). Variations between bacterial (B-ARISA) and fungal (F-ARISA) community structure were quantified b…

Dynamique des intéractions plante-microorganismes dans la rhizosphère: vers une meilleure prise en compte du fonctionnement de la plante et conséquence évolutive

Qu’attendre des recherches en microbiologie du sol ?

SPE EA EcolDur GenoSol MERS IPM Résumé du livre : La fertilité des sols est au carrefour des enjeux de sécurité alimentaire, de protection de l’environnement et de rentabilité économique de l’activité agricole. Cet ouvrage présente les résultats d’une réflexion prospective sur le contexte de la fertilisation dans les 5-10 ans à venir. Il définit les besoins en termes de méthodes et d'outils pour la gestion des cycles biogéochimiques et le raisonnement de la fertilisation en agriculture. Mots clés du livre : agriculture - agronomie - eau - effluent - engrais - environnement - fertilisation - pollution - prévention - production végétale - prospective - sol Description du chapitre 10 (partie 3…

A mathematical method for determining genome divergence and species delineation using AFLP.

The delineation of bacterial species is presently achieved using direct DNA-DNA relatedness studies of whole genomes. It would be helpful to obtain the same genomically based delineation by indirect methods, provided that descriptions of individual genome composition of bacterial genomes are obtained and included in species descriptions. The amplified fragment length polymorphism (AFLP) technique could provide the necessary data if the nucleotides involved in restriction and amplification are fundamental to the description of genomic divergences. Firstly, in order to verify that AFLP analysis permits a realistic exploration of bacterial genome composition, the strong correspondence between …

A core microbiota of plant and earthworm interaction? Phylogenetic and functional aspects

International audience; The core microbiota concept has been proposed to describe the subset of a microbiota (e.g. the rhizosphere microbial community) associated with a given host (e.g. a plant) going beyond macroenvironment differences (e.g. soil type), and characterized by taxonomic markers (e.g. 16S rRNA gene sequences). Its existence has been questioned by geographical studies, showing the overruling soil type effect in shaping microbial communities. As far as biotic determinants are concerned, several “hosts” or macroorganisms are impacting a given habitat and its specific microbial community. In soils, there is an overlap between the so-called rhizosphere and the drilosphere, defined…

Bacterial community diversity harboured by interacting species

International audience; All animals are infected by microbial partners that can be passengers or residents and influence many biological traits of their hosts. Even if important factors that structure the composition and abundance of microbial communities within and among host individuals have been recently described, such as diet, developmental stage or phylogeny, few studies have conducted cross-taxonomic comparisons, especially on host species related by trophic relationships. Here, we describe and compare the microbial communities associated with the cabbage root fly Delia radicum and its three major parasitoids: the two staphylinid beetles Aleochara bilineata and A. bipustulata and the…

Seasonal fluctuations and long-term persistence of pathogenic populations of Agrobacterium spp. in soils.

ABSTRACT Short- and long-term persistence of pathogenic (i.e., tumor forming) agrobacteria in soil was investigated in six nursery plots with a history of high crown gall incidence. No pathogenic Agrobacterium strains were isolated in soil samples taken in fall and winter in any plots, but such strains were isolated from both bulk soils and weed rhizospheres (over 0.5 × 10 5 pathogenic CFU/g of bulk soil or rhizosphere) in three out of six plots in spring and summer. PCR amplifications of a vir sequence from DNA extracted from soil confirmed the presence of Ti plasmids in summer and their absence in fall and winter. The results indicate that strains that harbor a Ti plasmid had an unforesee…

Implication of pyoverdines in the interactions of fluorescent pseudomonads with soil microflora and plant in the rhizosphere

International audience

Monitoring microbial diversity in European soils: ongoing projects and challenges

SPEEcolDurGenoSolCT3communication orale invitée, résumé et slides; According to the Convention of Biological Diversity (Rio de Janeiro, 1992), biodiversity is the variation in life from genes to species, communities, ecosystems, and landscapes. Soils represent a huge reservoir of biodiversity which varies in terms of taxonomic richness, relative abundance and distribution according to soil types, climatic conditions, vegetation and land uses. The key functions supporting ecosystem services as identified in the Millennium Ecosystem Assessment (MEA, 2005) largely depend upon organisms that inhabit the soil. Thus, the design and implementation of a sustainable soil management strategy requires…

Reciprocal interactions between plants and fluorescent pseudomonads in relation with iron in the rhizosphere

National audience; Although iron is the fourth element in the Earth’s crust, the availability of Fe(III) is limited in most cultivated soils due to their pH. In soil adhering to plant roots (rhizosphere), plants release a sgnificant part of their photosynthetates (rhizodeposits) that promote microbial density and activity. Iron uptake by this microflora and by plant roots contributes to decrease even more iron availability in the rhizosphere. In this competition context, plants and microbes have developed active strategies of iron uptake. In dicotyledon plants, this strategy involves (i) the excretion of protons, (ii) the reduction of Fe(III) by reductases, and (iii) plasmalemma transport o…

Reciprocal interactions between plants and fluorescent pseudomonads in relation with iron in the rhizosphere

International audience; Iron is an essential element for plants and microbes. However, in most cultivated soils, the concentration of iron available for these living organisms is very low since its solubility is controlled by stable hydroxides, oxyhydroxides and oxides. The high demand for iron by plants and microorganisms in the rhizosphere together with its low availability in soils leads to a strong competition for this nutrient among living organisms. To face this competition, plants and microorganisms have developed active strategies of iron uptake. In non graminaceous plants (strategy I), iron uptake relies on acidification and reduction of Fe+++ in Fe++ which incorporated in the root…