This polyphasic taxonomic study reassessed the genus Aneurinibacillus using 53 bacterial strains representing 25 species, with emphasis on endospore-forming bacteria from rRNA group 4. Researchers employed multiple characterization methods including amplified ribosomal DNA restriction analysis (ARDRA), fatty acid methyl ester analysis, protein electrophoresis, pyrolysis mass spectrometry, and phenotypic tests. ARDRA analysis confirmed that Aneurinibacillus aneurinilyticus and A. migulanus form a distinct cluster separate from Brevibacillus species. Bacillus thermoaerophilus was found to cluster most closely with Aneurinibacillus rather than other Bacillus groups, leading to its reclassification as A. thermoaerophilus. The two Aneurinibacillus species are phenotypically and genotypically similar but distinguishable by several characters including spore morphology, casein/gelatin hydrolysis, and carbon source assimilation patterns. Emended descriptions are provided for A. aneurinilyticus, A. migulanus, and the newly transferred A. thermoaerophilus, with phenotypic characteristics useful for genus-level differentiation also presented.

Key findings

• Bacillus thermoaerophilus was reclassified as Aneurinibacillus thermoaerophilus based on ARDRA analysis showing closer relationship to Aneurinibacillus than other Bacillus groups
• Aneurinibacillus aneurinilyticus and A. migulanus are phenotypically and genotypically similar but can be distinguished by spore morphology, enzyme production, and carbon source assimilation patterns
• The Aneurinibacillus genus is distinctly separate from Brevibacillus at the molecular level, as confirmed by ARDRA and pyrolysis mass spectrometry analysis
• Multiple phenotypic characters including hydrolysis of casein and gelatin, growth temperature tolerance, and assimilation of specific carbon sources differentiate Aneurinibacillus species from Brevibacillus species