Summary auto-generated
Researchers isolated a novel Bacillus species, strain CBD 119T, from a white powder suspected of containing Bacillus anthracis during the 2001 anthrax bioterrorism aftermath. While the isolate tested negative for B. anthracis through conventional and molecular methods, it unusually contained plasmid-borne genes from B. anthracis's pX02 virulence plasmid, including capsule-encoding genes with up to 100% nucleotide identity to B. anthracis sequences. This was the first report of pX02 capsule genes in a Bacillus species outside the B. cereus group. Phylogenetic analysis based on 16S rRNA gene sequencing showed 99.3% similarity to Bacillus luciferensis, but comprehensive polyphasic taxonomy revealed significant differences. DNA-DNA hybridization yielded only 12.9-17.9% relatedness compared to the 70% threshold for species designation. The isolate differed from B. luciferensis in 18 of 96 phenotypic traits, including motility, endospore morphology, and pH optimum. Notably, CBD 119T showed accelerated growth at acidic pH (5.9), distinguishing it as a separate species. Based on these molecular and phenotypic distinctions, the researchers propose Bacillus acidiceler sp. nov. as a new species designation.
Key findings
- A novel Bacillus species, Bacillus acidiceler, was isolated from a forensic specimen and represents the first Bacillus species outside the B. cereus group documented to carry B. anthracis pX02 plasmid genes including capsule-encoding sequences.
- Despite 99.3% 16S rRNA gene sequence similarity to Bacillus luciferensis, DNA-DNA hybridization showed only 12.9-17.9% relatedness, well below the 70% species threshold, justifying new species designation.
- Bacillus acidiceler exhibits an acidic pH optimum (5.8-6.3) with accelerated growth at pH 5.9 compared to neutral pH, distinguishing it ecologically from related species.
- The isolate differs from B. luciferensis in 18 of 96 phenotypic traits including motility, endospore swelling patterns, and temperature growth range, supporting polyphasic taxonomic differentiation.
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Abstract
Research at the Center for Biological Defense identified plasmid-borne forms of Bacillus anthracis pXO2 genes in a Gram-positive, endospore-forming rod, isolated from a forensic specimen considered a credible threat of harbouring anthrax. Conventional, commercial and molecular-based methods indicated that the isolate (CBD 119T) was not B. anthracis and considered not to be a member of the Bacillus cereus group. Based on the 16S rRNA gene sequence similarities, strain CBD 119T was most closely related to Bacillus luciferensis LMG 18422T (99.3 %). Phenotyping and fatty acid methyl ester analysis of the isolate were conducted alongside B. luciferensis JCM 12212T. The major cellular fatty acids (anteiso-C15 : 0, iso-C15 : 0, and >7 iso or anteiso forms) supported inclusion of the isolate in the genus Bacillus. Strain CBD 119T was inconsistent with B. luciferensis JCM 12212T for 18 of 96 traits evaluated including motility, degree of endospore-driven swelling and pH optimum; the two were linked by fatty acid methyl ester analysis as separate but closely related species. DNA–DNA relatedness between strain CBD 119T and B. luciferensis JCM 12212T resulted in less than 20 % hybridization. The results of biochemical and physiological characterization, chemotaxonomic analysis and DNA–DNA hybridization differentiated strain CBD 119T both phenotypically and genotypically from the only species with validly published name with greater than 97 % 16S rRNA gene sequence similarity. The isolate has an accelerated doubling time when grown in aerated broth at pH 5.9 relative to that at pH 7.1. Therefore, it is proposed that strain CBD 119T represents a novel species, Bacillus acidiceler sp. nov. The type strain is strain CBD 119T (=NRRL B-41736T=DSM 18954T).