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Aragno, Michel

Nom
Aragno, Michel
Affiliation principale
Email
Michel.Aragno@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/753

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  • Publication
    Accès libre
    Spatio-temporal dynamics of bacterial communities associated with two plant species differing in organic acid secretion: A one-year microcosm study on lupin and wheat
    (2008)
    Weisskopf, Laure
    ;
    Le Bayon, Renée-Claire 
    ;
    Kohler, Florian
    ;
    Page, Valérie
    ;
    Jossi, Maryline
    ;
    Gobat, Jean-Michel 
    ;
    Martinoia, Enrico
    ;
    Aragno, Michel 
    Plants are generally assumed to influence the surrounding soil microflora through rhizodeposition. However, the role of rhizodeposits, and especially organic acids, in structuring the bacterial communities is still poorly understood. In this study, we asked the question whether plants differing in organic acid secretion have a different impact on the soil bacterial communities, and if this is the case, to which extent this impact is due to different organic acid concentrations in the rhizosphere. To investigate this question, we compared white lupin and wheat. The former is a high organic acid-secreting species, while the latter secretes only low amounts of carboxylates. We grew the plants in large microcosms including root-free control compartments for one year (replanted every second month) and analyzed the spatio-temporal changes in soil ATP concentrations, as well as in diversity and structure of bacterial communities (using DNA- and RNA-based DGGE) along a root-soil gradient after two, six and twelve month's cultivation. Our results showed: i) that white lupin and wheat differed in their impact on soil ATP concentrations and on the structure of root bacterial communities; ii) that cultivation time was a key factor in explaining the observed differences in all the parameters studied; and iii) that the amounts of organic acids accounted for a significant proportion (15%) of the variability within root active communities. These results indicate that plants influence their associated bacterial communities in a species-specific way and that for communities living in the direct vicinity of roots (rhizoplane-endorhizosphere), a significant part of this influence can be attributed to root-secreted organic acids.
  • Publication
    Accès libre
    Plant growth stage, fertiliser management and bio-inoculation of arbuscular mycorrhizal fungi and plant growth promoting rhizobacteria affect the rhizobacterial community structure in rain-fed wheat fields
    (2006)
    Roesti, David
    ;
    Gaur, Rachna
    ;
    Johri, B. N.
    ;
    Imfeld, G.
    ;
    Sharma, S.
    ;
    Kawaljeet, K.
    ;
    Aragno, Michel 
    The goal of this study was first to assess the dynamics of the bacterial community during a growing season in three Indian rain-fed wheat fields which differ mainly through their fertilizer management and yield and then to study the effects of PGPR/AMF bio-inoculations on the bacterial community structure and wheat growth. The bacterial community structure of the rhizosphere soil (RS) and the rhizoplane/endorhizosphere (RE) was determined by PCR-denaturing gradient gel electrophoresis. Seed treatments consisted of consortia of two PGPR strains alone or combined with AMF or AMF alone. The PGPR strains were Pseudomonas spp. which included some or all of the following plant growth promoting properties: phosphate solubilisation and production of indole-3-acetic acid, siderophores, 1-aminocyclopropane-1-carboxylate deaminase and diacetyl-phloroglucinol. The mycorrhizal inoculum was an indigenous AMF consortium isolated from the field with the lowest level of fertilization and yield. Variation partitioning analysis of the DGGE data indicated a predominant effect of the wheat growth stage (30.4% of the variance, P=0.001) over the type of field (9.0%, P=0.027) on the bacterial community structure in the RE. The impact of plant age in the RS was less than in the RE and the bacterial community structure of the field with the highest input of fertilization was very different from the low input fields. The bio-inoculants induced a significant modification in the bacterial community structure. In the RS, the bacterial consortia explained 28.3% (P=0.001) and the presence of AMF 10.6% (P=0.02) of the variance and the same trend was observed in the RE. Plant yield or grain quality was either increased or remained unaffected. For example, protein content was significantly higher in the treated plants' grain compared to the control plants; maximum values were obtained when the PGPR were co-inoculated with the AMF. The percentage of root colonization by AMF was significantly higher in the treatments containing a mycorrhizal inoculum than in the untreated control and remained unaffected by the PGPR treatments. In conclusion, the wheat rhizobacterial community structure is highly dynamic and influenced by different factors such as the plant's age, the fertilizer input and the type of bio-inoculant. In addition, there is a distance-related effect of the root on the bacterial community. Finally, a combined bio-inoculation of diacetyl-phloroglucinol producing PGPR strains and AMF can synergistically improve the nutritional quality of the grain without negatively affecting mycorrhizal growth.
  • Publication
    Accès libre
    Nitrogen fertiliser rate affects the frequency of nitrate-dissimilating Pseudomonas spp. in the rhizosphere of Lolium perenne grown under elevated pCO2 (Swiss FACE)
    (2005)
    Fromin, Nathalie
    ;
    Tarnawski, Sonia Estelle
    ;
    Roussel-Delif, L.
    ;
    Hamelin, Jérôme
    ;
    Baggs, E.M.
    ;
    Aragno, Michel 
    The effect of elevated pCO2 (60 Pa) on the frequency of nitrate-dissimilating Pseudomonas (NDP) was investigated in the rhizosphere of fertilised Lolium perenne swards in the Swiss Free Air Carbon dioxide Enrichment (FACE) experiment. Numbers of cultivable root-associated Pseudomonas were greater under elevated (60 Pa) than under ambient (36 Pa) pCO2 in both high and low N-fertilised swards. For both pCO2 conditions, the NDP frequency decreased with closer root proximity to L. perenne roots in low fertilised swards. Anyway, in high N swards the NDP frequency was similar in root and soil fractions. Thus, N availability may be a major factor influencing NDP populations under elevated pCO2, most likely due to increased competition for N between plant and nitrate-dissimilating bacteria.
  • Publication
    Accès libre
    Examination of Gould’s modified S1 (mS1) selective medium and Angle’s non-selective medium for describing the diversity of Pseudomonas spp. in soil and root environments
    (2003)
    Tarnawski, Sonia Estelle
    ;
    Hamelin, Jérôme
    ;
    Locatelli, Laurent
    ;
    Aragno, Michel 
    ;
    Fromin, Nathalie
    Studies on the diversity of environmental culturable Pseudomonas populations are dependent on the isolation procedure. This procedure includes the use of selective media which may influence the recovery of strains and thus the diversity described. In this study, we assessed the use of two agar isolation media for describing the diversity of soil- and root-inhabiting Pseudomonas associated with the perennial grass Molinia coerulea. A total of 382 Pseudomonas strains were recovered on either non-selective Angle’s medium, or on Gould’s modified S1 (mS1) Pseudomonas-selective medium. Their diversity was assessed by restriction analysis of PCR (polymerase chain reaction)-amplified 16S–23S rDNA internal transcript spacer sequences. The comparison of mS1- and Angle-recovered populations showed that the use of mS1 selective medium led to an underestimation of both Pseudomonas counts and diversity, especially in the soil environment.