Occurrence and diversity of bacterial communities in Tuber magnatum during truffle maturation

Authors

  • Elena Barbieri,

    Corresponding author
    1. Istituto di Chimica Biologica ‘Giorgio Fornaini’, Via Saffi, 2, University of Urbino ‘Carlo Bo’, 61029 Urbino, Italy.
      *E-mail v.stocchi@uniurb.it or barbieri@uniurb.it; Tel. (+39) 0722 305262; Fax (+39) 0722 320188.
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    • Authors have equally contributed to this work.

  • Chiara Guidi,

    1. Istituto di Chimica Biologica ‘Giorgio Fornaini’, Via Saffi, 2, University of Urbino ‘Carlo Bo’, 61029 Urbino, Italy.
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    • Authors have equally contributed to this work.

  • Joanne Bertaux,

    1. INRA Centre de Nancy, UMR1136 INRA–UHP Interaction Arbres-Microorganismes, Centre INRA de Nancy, Champenoux, 54280, France.
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    • Present address: Institut für Zoologie der Technischen Universität Darmstadt, Fachbereich 10, Biologie, Schnittspahnstraße 3, D-64287 Darmstadt, Germany.

  • Pascale Frey-Klett,

    1. INRA Centre de Nancy, UMR1136 INRA–UHP Interaction Arbres-Microorganismes, Centre INRA de Nancy, Champenoux, 54280, France.
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  • Jean Garbaye,

    1. INRA Centre de Nancy, UMR1136 INRA–UHP Interaction Arbres-Microorganismes, Centre INRA de Nancy, Champenoux, 54280, France.
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  • Paola Ceccaroli,

    1. Istituto di Chimica Biologica ‘Giorgio Fornaini’, Via Saffi, 2, University of Urbino ‘Carlo Bo’, 61029 Urbino, Italy.
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  • Roberta Saltarelli,

    1. Istituto di Chimica Biologica ‘Giorgio Fornaini’, Via Saffi, 2, University of Urbino ‘Carlo Bo’, 61029 Urbino, Italy.
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  • Alessandra Zambonelli,

    1. Dipartimento di Protezione e Valorizzazione Agroalimentare, Via Fanin 46, University of Bologna, 40127 Bologna, Italy.
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  • Vilberto Stocchi

    Corresponding author
    1. Istituto di Chimica Biologica ‘Giorgio Fornaini’, Via Saffi, 2, University of Urbino ‘Carlo Bo’, 61029 Urbino, Italy.
      *E-mail v.stocchi@uniurb.it or barbieri@uniurb.it; Tel. (+39) 0722 305262; Fax (+39) 0722 320188.
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*E-mail v.stocchi@uniurb.it or barbieri@uniurb.it; Tel. (+39) 0722 305262; Fax (+39) 0722 320188.

Summary

Tuber magnatum, an ascomycetous fungus and obligate ectomycorrhizal symbiont, forms hypogeous fruit bodies, commonly called Italian white truffles. The diversity of bacterial communities associated with T. magnatum truffles was investigated using culture-independent and -dependent 16S rRNA gene-based approaches. Eighteen truffles were classified in three groups, representing different degrees of ascocarp maturation, based on the percentage of asci containing mature spores. The culturable bacterial fraction was (4.17 ± 1.61) × 107, (2.60 ± 1.22) × 107 and (1.86 ± 1.32) × 106 cfu g−1 for immature, intermediate and mature ascocarps respectively. The total of bacteria count was two orders of magnitude higher than the cfu g−1 count. Sequencing results from the clone library showed a significant presence of α-Proteobacteria (634 of the 771 total clones screened, c. 82%) affiliated with Sinorhizobium, Rhizobium and Bradyrhizobium spp. The bacterial culturable fraction was generally represented by γ-Proteobacteria (210 of the 384 total strains isolated, c. 55%), which were mostly fluorescent pseudomonads. Fluorescent in situ hybridization confirmed that α-Proteobacteria (85.8%) were the predominant components of truffle bacterial communities with β-Proteobacteria (1.5%), γ-Proteobacteria (1.9%), Bacteroidetes (2.1%), Firmicutes (2.4%) and Actinobacteria (3%) only poorly represented. Molecular approaches made it possible to identify α-Proteobacteria as major constituents of a bacterial component associated with T. magnatum ascoma, independently from the degree of maturation.

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