Summary auto-generated
Takeuchi and Hatano conducted a phylogenetic study comparing 16S rRNA gene sequences from 19 bacterial strains, including representatives of Aureobacterium and Microbacterium species, along with related actinobacteria. Analysis of 43 total strains revealed that all Aureobacterium and Microbacterium species form a single monophyletic cluster with sequence similarity of 96.8-99.7%, in which species from both genera are intermixed rather than clustering separately. Despite historical separation based primarily on differences in cell wall diamino acids (lysine in Microbacterium versus ornithine in Aureobacterium), the strains showed very similar physiological, biochemical, and chemotaxonomic properties. The authors identified unique 16S rDNA signature nucleotides characteristic of this combined lineage. Based on high phylogenetic coherence and shared characteristics including similar menaquinones, fatty acid profiles, and DNA G+C content, the authors proposed merging the two genera into a redefined genus Microbacterium, following precedent in other actinobacteria. All thirteen validated Aureobacterium species were transferred to Microbacterium with new combinations, and the genus description was emended to accommodate organisms with either lysine or ornithine in their peptidoglycan.
Key findings
- 16S rRNA gene sequence analysis of 43 strains showed Aureobacterium and Microbacterium species form a single monophyletic cluster with high sequence similarity (96.8-99.7%), with species from both genera intermixed rather than separate
- Aureobacterium and Microbacterium species share similar chemotaxonomic and phenotypic characteristics including menaquinones (MK-11, 12, 13, 14), fatty acid profiles, and DNA G+C content (65-76 mol%)
- Cell wall diamino acid differences (lysine vs ornithine) do not reflect phylogenetic relationships and therefore should not be the primary basis for genus separation
- Unique 16S rDNA signature nucleotides were identified that characterize the Microbacterium-Aureobacterium lineage and distinguish it from other Microbacteriaceae genera
- The two genera were merged into a redefined genus Microbacterium, with all thirteen validated Aureobacterium species transferred to Microbacterium with new species combinations
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Abstract
The 16S rRNA gene sequences of 19 strains, 11 strains representing validated Aureobacterium or Microbacterium species and eight strains of non-valid species or isolates, were determined. These sequences were aligned with the sequences of other validated Aureobacterium and Microbacterium species and related actinobacteria. A comparative sequence analysis of 43 strains revealed that the species of the genera Aureobacterium and Microbacterium form a monophyletic association in which species of both genera are intermixed. The high similarity in phylogenetic properties found in the species within both genera and the close relationship in physiological and chemotaxonomic features other than the diamino acid in the cell wall, provided strong evidence that the genera Aureobacterium and Microbacterium should be unified. An emended genus Microbacterium is proposed for the two combined genera. The following validated Aureobacterium species were combined to the genus Microbacterium: Aureobacterium arabinogalactanolyticum to Microbacterium arabinogalactanolyticum, Aureobacterium barkeri to Microbacterium barkeri, Aureobacterium esteraromaticum to Microbacterium esteraromaticum, Aureobacterium flavescens to Microbacterium flavescens, Aureobacterium keratanolyticum to Microbacterium keratanolyticum, Aureobacterium liquefaciens to Microbacterium liquefaciens, Aureobacterium luteolum to Microbacterium luteolum, Aureobacterium saperdae to Microbacterium saperdae, Aureobacterium schleiferi to Microbacterium schleiferi, Aureobacterium terrae to Microbacterium terrae, Aureobacterium terregens to Microbacterium terregens, Aureobacterium testaceum to Microbacterium testaceum, and Aureobacterium trichothecenolyticum to Microbacterium trichothecenolyticum.