Bacillus weihenstephanensis characteristics are present in Bacillus cereus and Bacillus mycoides strains

The Bacillus cereus group comprises seven bacterial species: Bacillus cereus, Bacillus anthracis, Bacillus thuringiensis, Bacillus mycoides, Bacillus pseudomycoides, Bacillus cytotoxicus, and Bacillus weihenstephanensis. Bacillus weihenstephanensis is distinguished based on its capability to grow at 7 °C but not at 43 °C, and the presence of specific signature sequences in the 16S rRNA and cspA genes and in several housekeeping genes: glpF, gmK, purH, and tpi. Bacillus weihenstephanensis-specific signature sequences were found in some B. cereus and B. mycoides strains suggesting psychrotolerance. This was confirmed by growth at 7 °C but not at 43 °C. The other B. cereus and B. mycoides strains and all B. anthracis, B. thuringiensis, and B. pseudomycoides harbored the mesophilic signature sequences. The strains tested grew at 43 °C but did not grow at 7 °C. A maximum-likelihood phylogenetic tree was inferred from comparisons of the concatenated nucleotide sequences. Three groups and one branch were revealed. Group I, II, and III comprised the mesophilic B. cereus, some mesophilic B. mycoides, and all B. anthracis and B. thuringiensis strains; the psychrotolerant B. cereus and B. mycoides, and all B. weihenstephanensis strains; and some mesophilic B. mycoides and all B. pseudomycoides strains, respectively. The branch corresponds to the single B. cytotoxicus strain. Based on psychrotolerance and multilocus sequence analysis, further confirmed by comparisons of amino acid sequences, we show that some B. cereus and B. mycoides strains should be reclassified as B. weihenstephanensis. © 2013 Federation of European Microbiological Societies.