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Appl. Environ. Microbiol., 11 1997, 4331-4339, Vol 63, No. 11
T Hurek, B Wagner and B Reinhold-Hurek
Most species of the diazotrophic Proteobacteria Azoarcus spp. occur in
association with grass roots, while A. tolulyticus and A. evansii are soil
bacteria not associated with a plant host. To facilitate species
identification and strain comparison, we developed a protocol for PCR-
generated genomic fingerprints, using an automated sequencer for fragment
analysis. Commonly used primers targeted to REP (repetitive extragenic
palindromic) and ERIC (enterobacterial repetitive intergenic consensus)
sequence elements failed to amplify fragments from the two species tested.
In contrast, the BOX-PCR assay (targeted to repetitive intergenic sequence
elements of Streptococcus) yielded species-specific genomic fingerprints
with some strain-specific differences. PCR profiles of an additional PCR
assay using primers targeted to tRNA genes (tDNA-PCR, for tRNA(IIe)) were
more discriminative, allowing differentiation at species-specific (for two
species) or infraspecies- specific level. Our protocol of several
consecutive PCR assays consisted of 16S ribosomal DNA (rDNA)-targeted,
genus-specific PCR followed by BOX- and tDNA-PCR; it enabled us to assign
new diazotrophic isolates originating from fungal resting stages
(sclerotia) to known species of Azoarcus. The assignment was confirmed by
phylogenetic analysis of 16S rDNA sequences. Additionally, the phylogenetic
distances and the lack of monophyly suggested emendment of the genus
Azoarcus: the unnamed species Azoarcus groups C and D and a new group (E)
of Azoarcus, which was detected in association with fungi, are likely to
have the taxonomic rank of three different genera. According to its small
subunit rRNA, the sclerotium-forming basidiomycete was related to the
Ustilagomycetes, facultatively biotrophic parasites of plants. Since they
occurred in a field which was under cultivation with rice and wheat, these
fungi might serve as a niche for survival for Azoarcus in the soil and as a
source for reinfection of plants.
Copyright © 1997, American Society for Microbiology
Identification of N2-fixing plant- and fungus-associated Azoarcus species by PCR-based genomic fingerprints
Max-Planck-Institut fur Terrestrische Mikrobiologie, Arbeitsgruppe, Marburg, Germany.
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