Some (bacilli) like it hot: genomics of Geobacillus species

The genus Geobacillus includes thermophilic Grampositive spore-forming bacteria that form a phylogenetically coherent clade within the family Bacillaceae. They are of great interest for biotechnology (as discussed below). These thermophiles seem to be ubiquitous; viable Geobacillus spores can be isolated in large quantities not only from hot environments such as hydrothermal vents, but also, paradoxically, from cool soils and cold ocean sediments (Zeigler, 2014). These bacteria were previously categorized as ‘Group 5’ within the genus Bacillus but were subsequently split into the new genus Geobacillus (Nazina et al., 2001). Many Geobacillus strains were previously described as belonging to a single species Bacillus stearothermophilus, but it was clear that there was great heterogeneity in physiology, preferred temperature range and other phenotypic characteristics among these strains. For example, see Fig. 1 showing three distinct colony morphologies among three strains described as ‘B. stearothermophilus’. It is now absolutely clear that there are several distinct species within Geobacillus and these can be distinguished by both genotype and phenotype (Nazina et al., 2001; Banat et al., 2004; Zeigler, 2005; Dinsdale et al., 2011; Coorevits et al., 2012).