Summary auto-generated
This study reclassifies two bacterial strains previously identified as Brevibacillus brevis based on comprehensive molecular and phenotypic analysis. Researchers examined 29 strains labeled as B. brevis and analyzed their 16S rRNA gene hypervariable regions, finding they belonged to multiple distinct species across Brevibacillus, Aneurinibacillus, and Bacillus genera. Two strains—NCIMB 13288 and DSM 6472—showed low DNA-DNA relatedness (<14%) and distinct 16S rRNA sequences (96.8-97.9% and 95.4-98.8% similarity, respectively) compared to related species. NCIMB 13288 clustered with Aneurinibacillus species and displayed thermophilic growth (45-50°C optimal), while DSM 6472 clustered with Brevibacillus species with mesophilic growth (30-35°C optimal). Both shared menaquinone-7 as their major quinone and had distinct fatty acid profiles. The study proposes naming NCIMB 13288 as Aneurinibacillus danicus sp. nov. and DSM 6472 as Brevibacillus limnophilus sp. nov., reviving the latter name from its original 1940 designation as 'Bacillus limnophilus'. These findings highlight ongoing taxonomic challenges within spore-forming bacteria and emphasize the importance of polyphasic taxonomy for accurate species identification.
Key findings
- Two strains previously misidentified as Brevibacillus brevis represent novel species: Aneurinibacillus danicus (NCIMB 13288, thermophilic) and Brevibacillus limnophilus (DSM 6472, mesophilic)
- DNA-DNA hybridization and 16S rRNA sequence analysis revealed low relatedness (<14%) of these strains to existing species within their respective genera
- Analysis of 29 B. brevis strains showed heterogeneity, with 13 clustering with Aneurinibacillus, 8 with Bacillus methanolicus, and only 8 with true Brevibacillus species
- The 16S rRNA hypervariable region proved useful for rapid identification and differentiation of Aneurinibacillus and Brevibacillus species
- Both novel species exhibited menaquinone-7 as their primary respiratory quinone with distinct fatty acid profiles distinguishing them from related species
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Abstract
Comparison of the hypervariable region (269279 bases in length) at the 5' end of the 16S rDNA sequences of 29 bacterial strains that were identified previously as Brevibacillus brevis showed that 13 strains clustered with Aneurinibacillus species, eight strains clustered with Bacillus species and eight strains clustered with Brevibacillus species. Based on DNADNA hybridization results, 27 strains, not including [Brevibacillus brevis] NCIMB 13288 and [Brevibacillus brevis] DSM 6472, were reidentified as Aneurinibacillus migulanus, Aneurinibacillus thermoaerophilus, Bacillus methanolicus, Bacillus oleronius, Brevibacillus agri, Brevibacillus brevis and Brevibacillus parabrevis. [Brevibacillus brevis] NCIMB 13288, which was located in the Aneurinibacillus cluster, showed low DNADNA relatedness (<14 %) and low 16S rDNA sequence similarity (96·897·9 %) to other Aneurinibacillus species. [Brevibacillus brevis] DSM 6472, which was located in the Brevibacillus cluster, also showed low DNADNA relatedness (<12 %) and low 16S rDNA sequence similarity (95·498·8 %) to other Brevibacillus species. These genotypic and phylogenetic data, plus phenotypic and chemotaxonomic characteristics, suggest that [Brevibacillus brevis] NCIMB 13288 (=IAM 15048) and [Brevibacillus brevis] DSM 6472 (=NRRL NRS-887) represent novel species of the genera Aneurinibacillus and Brevibacillus, respectively, for which the names Aneurinibacillus danicus sp. nov. and Brevibacillus limnophilus sp. nov. are proposed.