The phylogenetic diversity of thermophilic members of the genus Bacillus as revealed by 16S rDNA analysis

Sixteen thermophilic strains of the genus Bacillus, representing eight validly described and six invalidly described species, as well as one unassigned strain, were investigated by comparative 16S rDNA analyses and the sequences compared to the existing database for the genera Bacillus and Alicyclobacillus. The majority of strains were found to cluster in two groups represented by B. stearothermophilus and B. pallidus. Bacillus smithii, B. thermocloacae, and B. thermoruber are phylogenetically well separated and cluster within the radiation of mesophilic bacilli. The as yet undescribed taxon ‘B. flavothermus’ warrants species status. B. schlegelii and B. tusciae group peripherally with members of Alicyclobacillus and may be reclassified when more phenotypic data support their phylogenetic position.