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A N2-fixing endophytic Burkholderia sp. associated with maize plants cultivated in Mexico

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Abstract:

In the frame of a survey of potentially endophytic N2-fixing Burkholderia associated with maize in Mexico, its country of origin, the soil of an indigenous maize field near Oaxaca was studied. Under laboratory conditions, plant seedlings of two ancient maize varieties were used as a trap to select endophyte candidates from the soil sample. Among the N2 fixers isolated from inside plant tissues and able to grow on PCAT medium, the most abundant isolates belonged to genus Burkholderia (API 20NE, rrs sequences). Representative isolates obtained from roots and shoots of different plants appeared identical (rrs and nifH RFLP), showing that they were closely related. In addition, their 16S rDNA sequences differed from described Burkholderia species and, phylogenetically, they constituted a separate deep-branching new lineage in genus Burkholderia. This indicated that these isolates probably constituted a new species. An inoculation experiment confirmed that these N2-fixing Burkholderia isolates could densely colonize the plant tissues of maize. More isolates of this group were subsequently obtained from field-grown maize and teosinte plants. It was hypothesized that strains of this species had developed a sort of primitive symbiosis with one of their host plants, teosinte, which persisted during the domestication of teosinte into maize.Key words: endophytic bacteria, nitrogen-fixation, Zea mays, Burkholderia.

Lors d'une étude des Burkholderia endophytes fixatrices d'azote associées au maïs dans son pays d'origine, le Mexique, le sol d'un champ de maïs traditionnel de la région d'Oaxaca a été étudié. Des jeunes plantes de maïs de deux variétés traditionnelles furent utilisées comme pièges, en conditions de laboratoire, pour sélectionner les souches candidates endophytes à partir du sol. Les tissus de ces plantes montrèrent la présence de bactéries fixatrices d'azote poussant sur le milieu PCAT, identifiées comme Burkholderia (API 20NE). Ces isolats présentaient des profils de restriction identiques pour les gènes nifH et rrs. Leurs séquences 16S rDNA différaient de celles des espèces connues de Burkholderia et l'étude de leur phylogénie a montré qu'ils constituaient un phylum séparé. Ces résultats suggèrent qu'ils constituent une nouvelle espèce de Burkholderia. Un essai d'inoculation en serre a montré que cette bactérie était bien capable de coloniser densément les tissus du maïs. De nouveaux isolats comparables furent obtenus ultérieurement de maïs au champ et même de téosinte. Ces résultats permettent d'émettre l'hypothèse que des souches de ce type de Burkholderia ont développé une sorte de symbiose primitive avec la téosinte, qui a été préservée durant sa domestication en maïs.Mots clés : bactéries endophytes, fixation d'azote, Zea mays, Burkholderia.

Keywords: Burkholderia; Zea mays; bactéries endophytes; endophytic bacteria; fixation d'azote; nitrogen-fixation

Document Type: Research Article

Publication date: April 1, 2002

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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