The 5 Clades of Bacillus
Most of the Gram-positive aerobic spore-forming bacteria were placed in the same genus, Bacillus. As a result, there are within the genus at least five clades containing organisms that are only distantly related (Figure 1). There are a number of sequenced Bacillus genomes include that of type strains of B. subtlis168, and the related alkaliphilic B. halodurans, a number pathogenic and nonpathogenic members of the B. cereus group (including B. cereus, B. anthracis, and B. thuringiensis) as well as environmental and industrial strains of B. licheniformis, B. clausii, Oceanobacillus iheyensis, and Geobacillus kaustophilus . Additionally, Sharon Lewis (Oklahoma University) is sequencing the thermophilic Bacillus stearothermophilus. So far, the sequenced Bacillus group members sequenced have a %G+C content around either 44% (B. subtilis, B. halodurans, B. licheniformis, B. clausii) or 35-36% (B. cereus group). The %G+C content (38-39%) of B. megaterium falls between these two groups. The genetic, biochemical and physiological characterization of B. megaterium is second among the Bacillus only to B. subtilis. These facts alone make B. megaterium a strong candidate for genome sequencing and comparative genomic analysis. Moreover, its successful use for many years as an industrial organism and its proven efficiency as a cloning host will be further enhanced by the availability of the genome sequence.