title: Bacteria of the genus Rhodopseudomonas (Bradyrhizobiaceae): obligate symbionts in mycelial cultures of the black truffles Tuber melanosporum and Tuber brumale.
abstract: BACKGROUND
  This work aimed at characterizing 12 isolates of the genus Tuber including Tuber melanosporum (11 isolates) and Tuber brumale (one isolate). This was done using internal transcribed spacer (ITS) sequences, confirming their origin.
  
  
  RESULTS
  Analysis of their mating type revealed that both MAT1-1 and MAT1-2 exist within these isolates (with 3 and 8 of each, respectively). We observed that each of these cultures was consistently associated with one bacterium that was intimately linked to fungal growth. These bacterial associates failed to grow in the absence of fungus. We extracted DNA from bacterial colonies in the margin of mycelium and sequenced a nearly complete 16S rDNA gene and a partial ITS fragment. We found they all belonged to the genus Rhodopseudomonas, fitting within different phylogenetic clusters. No relationships were evidenced between bacterial and fungal strains or mating types. Rhodopseudomonas being a sister genus to Bradyrhizobium, we tested the nodulation ability of these bacteria on a promiscuously nodulating legume (Acacia mangium), without success. We failed to identify any nifH genes among these isolates, using two different sets of primers.
  
  
  CONCLUSIONS
  While the mechanisms of interaction between Tuber and Rhodopseudomonas remain to be elucidated, their interdependency for in vitro growth seems a novel feature of this fungus.
authors.affiliation: CIRAD, UMR LSTM, 34398 Montpellier Cedex 5, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Le Roux
authors.affiliation: CIRAD, UMR LSTM, 34398 Montpellier Cedex 5, France.
authors.forename: Estelle
authors.initials: E
authors.lastname: Tournier
authors.affiliation: CIRAD, UMR LSTM, 34398 Montpellier Cedex 5, France.
authors.forename: Adrien
authors.initials: A
authors.lastname: Lies
authors.affiliation: CIRAD, UMR LSTM, 34398 Montpellier Cedex 5, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Sanguin
authors.affiliation: INRA Centre de Recherche de Clermont-Theix, 63039 Clermont-Ferrand Cedex, France.
authors.forename: Gérard
authors.initials: G
authors.lastname: Chevalier
authors.affiliation: IRD, UMR LSTM, 34398 Montpellier Cedex 5, France.
authors.forename: Robin
authors.initials: R
authors.lastname: Duponnois
authors.affiliation: Société d'Horticulture et d'Histoire Naturelle de l'Hérault, Parc à Ballon 1, bâtiment B, 125 rue du Moulin de Sémalen, 34000 Montpellier, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Mousain
authors.affiliation: CIRAD, UMR LSTM, 34398 Montpellier Cedex 5, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Prin
keywords: Ascomycete; Cultivability; In vitro production; Procaryote; Truffle