Summary auto-generated
This study employed comparative phylogenetic analysis of 16S rRNA and rpoB gene sequences to investigate the taxonomic relationships of nine Klebsiella species and related Enterobacteriaceae. The analysis revealed that the genus Klebsiella is heterogeneous and polyphyletic, consisting of three distinct phylogenetic clusters. Cluster I contained K. pneumoniae subspecies (pneumoniae, rhinoscleromatis, ozaenae) and K. granulomatis. Cluster II comprised K. ornithinolytica, K. planticola, K. trevisanii, and K. terrigena, which share the characteristic of growing at 10°C and utilizing L-sorbose as a carbon source. Cluster III contained only K. oxytoca. Based on these molecular findings combined with biochemical and DNA-DNA hybridization data, the authors propose dividing the genus Klebsiella into two genera and establishing a new genus Raoultella for cluster II species. The reorganization is supported by distinct phenotypic differences, with Raoultella species isolated primarily from environmental sources (plants, soil, water) while Klebsiella species are mainly recovered from mammalian mucosae. K. oxytoca remains in an uncertain taxonomic position.
Key findings
- The genus Klebsiella is polyphyletic and comprises three phylogenetic clusters that should be separated into at least two distinct genera: Klebsiella and the newly proposed Raoultella gen. nov.
- Cluster II species (K. ornithinolytica, K. planticola, K. trevisanii, K. terrigena) are reclassified as Raoultella and are characterized by growth at 10°C and L-sorbose utilization, distinguishing them from K. pneumoniae subspecies in Cluster I.
- K. planticola and K. trevisanii share 99.8-99.9% sequence similarity in both 16S rRNA and rpoB genes, supporting their combination as a single species.
- Phylogenetic clustering with 16S rRNA and rpoB sequences shows bootstrap values ≥70%, confirming the validity of the three-cluster organization and supporting genus-level differentiation.
- K. oxytoca forms a distinct third group with uncertain taxonomic position, possibly warranting placement in a separate unnamed genus.
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Abstract
The phylogenetic relationships of the type strains of 9 Klebsiella species and 20 species from 11 genera of the family Enterobacteriaceae were investigated by performing a comparative analysis of the sequences of the 16S rRNA and rpoB genes. The sequence data were phylogenetically analysed by the neighbour-joining and parsimony methods. The phylogenetic inference of the sequence comparison confirmed that the genus Klebsiella is heterogeneous and composed of species which form three clusters that also included members of other genera, including Enterobacter aerogenes, Erwinia clusters I and II and Tatumella. Cluster I contained the type strains of Klebsiella pneumoniae subsp. pneumoniae, Klebsiella pneumoniae subsp. rhinoscleromatis and Klebsiella pneumoniae subsp. ozaenae. Cluster II contained Klebsiella ornithinolytica, Klebsiella planticola, Klebsiella trevisanii and Klebsiella terrigena, organisms characterized by growth at 10 degrees C and utilization of L-sorbose as carbon source. Cluster III contained Klebsiella oxytoca. The data from the sequence analyses along with previously reported biochemical and DNA--DNA hybridization data support the division of the genus Klebsiella into two genera and one genogroup. The name Raoultella is proposed as a genus name for species of cluster II and emended definitions of Klebsiella species are proposed.