Summary auto-generated
This study characterized bacterial strains collected from soil and wheat roots using polyphasic taxonomy to identify and classify Ochrobactrum species. Researchers immunotrapped bacteria using monoclonal antibodies against Ochrobactrum anthropi and analyzed 700+ isolates using multiple approaches: REP-PCR fingerprinting, DNA-DNA hybridization, 16S rDNA sequencing, BIOLOG substrate utilization, and phenotypic testing. The analysis revealed that the isolated strains belonged to known species (O. anthropi and O. intermedium) or represented new species. Two novel species were formally described: Ochrobactrum tritici sp. nov. (type strain SCII24T), isolated exclusively from wheat rhizoplane samples and showing preference for this specific habitat, and Ochrobactrum grignonense sp. nov. (type strain OgA9aT), isolated from soil. Both new species were distinguished through separate DNA-DNA reassociation groups, distinct BIOLOG phenotypic clusters, diagnostic biochemical characteristics, and phylogenetic positioning. The study demonstrates the value of combined molecular and phenotypic approaches for accurate bacterial identification and reveals previously unrecognized diversity within the genus Ochrobactrum in agricultural environments.
Key findings
- Two novel Ochrobactrum species were discovered and formally described: O. tritici sp. nov., which colonizes wheat roots, and O. grignonense sp. nov., found in agricultural soil
- REP-PCR fingerprinting, DNA-DNA hybridization, and 16S rDNA analysis consistently grouped these new species separately from O. anthropi and O. intermedium, confirming their distinct status
- O. tritici showed habitat specificity, being isolated exclusively from wheat rhizoplane samples across multiple soil and cultivar combinations
- BIOLOG substrate utilization profiling identified diagnostic phenotypic differences between the species, including differential carbon source utilization patterns
- The study demonstrates that Ochrobactrum bacteria are common in agricultural soils and rhizospheres, with greater diversity than previously recognized by phenotypic methods alone
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Abstract
M Lebuhn, W Achouak, M Schloter, O Berge, H Meier, M Barakat, A Hartmann and T Heulin
DSV-DEVM, Laboratoire d'Ecologie Microbienne de la Rhizosphere, UMR163 CNRS-CEA, CEA Cadarache, F-13108 St Paul lez Durance, France
A large collection of bacterial strains, immunotrapped from soil and from the wheat rhizoplane, was subjected to polyphasic taxonomy by examining various pheno- and genotypic parameters. Strains were grouped on (inter) repetitive extragenic palindromic DNA (REP) PCR profiles at the intraspecies level. Pheno- and genotypic characters were assessed for representatives from 13 different REP groups. Strains of nine REP groups constituting two physiological BIOLOG clusters fell in the coherent DNA--DNA reassociation group of Ochrobactrum anthropi. Strains of two REP groups constituting a separate BIOLOG cluster fell in the coherent DNA--DNA reassociation group of Ochrobactrum intermedium. Additional phenotypic characters differentiating O. anthropi and O. intermedium were found. REP group K strains constituted a different BIOLOG cluster, a separate DNA--DNA reassociation group and a distinct phylogenetic lineage in 16S rDNA homology analysis, indicating that REP group K strains represent a new species. Diagnostic phenotypic characters were found. Closest relatives were Ochrobactrum species. The name Ochrobactrum grignonense sp. nov. is proposed (type strain OgA9a(T)=LMG 18954(T)=DSM 13338(T)). REP group J strains again constituted a different BIOLOG cluster, a separate DNA--DNA reassociation group and showed, as a biological particularity, a strict preference for the rhizoplane as habitat. Diagnostic phenotypic characters were found. This indicated that REP group J strains represent a further new species, although phylogenetic analyses using 16S rDNA homology were not able to separate the cluster of REP group J sequences significantly from 16S rDNA sequences of Ochrobactrum anthropi. The name Ochrobactrum tritici sp. nov. is proposed (type strain SCII24(T) = LMG 18957(T)= DSM 13340(T)).