Abstract
A previous analysis showed that Gammaproteobacteria could be the sole recoverable
bacteria from surface-sterilized nodules of three wild species of Hedysarum. In
this study we extended the analysis to eight Mediterranean native, uninoculated
legumes never previously investigated regarding their root-nodule microsymbionts.
The structural organization of the nodules was studied by light and
electron microscopy, and their bacterial occupants were assessed by combined
cultural and molecular approaches. On examination of 100 field-collected nodules,
culturable isolates of rhizobia were hardly ever found, whereas over 24 other
bacterial taxa were isolated from nodules. None of these nonrhizobial isolates
could nodulate the original host when reinoculated in gnotobiotic culture. Despite
the inability to culture rhizobial endosymbionts from within the nodules using
standard culture media, a direct 16S rRNA gene PCR analysis revealed that most of
these nodules contained rhizobia as the predominant population. The presence of
nodular endophytes colocalized with rhizobia was verified by immunofluorescence
microscopy of nodule sections using an Enterobacter-specific antibody. Hypotheses
to explain the nonculturability of rhizobia are presented, and pertinent literature
on legume endophytes is discussed.

Rosella Muresu1, Elisa Polone2, Leonardo Sulas1, Barbara Baldan3, Alessandra Tondello3, Giuseppe
Delogu4, Piero Cappuccinelli4, Sara Alberghini2, Yacine Benhizia5, Hayet Benhizia6, Ammar
Benguedouar5, Bruno Mori7, Roberto Calamassi7, Frank B. Dazzo8 & Andrea Squartini2

FEMS Microbiol Ecol 63 (2008) 383–400

这个研究对分析根瘤分离物及根瘤内生细菌的群落组成有一定的借鉴意义。

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