The Bacillus cereus group: novel aspects of population structure and genome dynamics

Abstract

Aims: To provide new insights into the population and genomic structure of the Bacillus cereus group of bacteria. Methods and Results: The genetic relatedness among B. cereus group strains was assessed by multilocus sequence typing (MLST) using an optimized scheme based on seven chromosomal housekeeping genes. A set of 48 strains from different clinical sources was included, and six clonal complexes containing several genetically similar isolates from unrelated patients were identified. Interestingly, several clonal groups contained strains that were isolated from similar human sources. Furthermore, comparative whole genome sequence analysis of 16 strains led to the discovery of novel ubiquitous genome features of the B. cereus group, such as atypical group II introns, IStrons, and hitherto uncharacterized repeated elements. Conclusions: The B. cereus group constitutes a coherent population unified by the presence of ubiquitous and specific genetic elements which do not show any pattern, either in their sequences or genomic locations, which allows to differentiate between the member species of the group. Nevertheless, the population is very dynamic, as particular lineages of clinical origin can evolve to form clonal complexes. At the genome level, the dynamic behaviour is indicated by the presence of numerous mobile and repeated elements. Significance and Impact of the Study: The B. cereus group of bacteria comprises species that are of medical and economic importance. The MLST data, along with the primers and protocols used, will be available in a public, web‐accessible database (http://mlstoslo.uio.no).

Genotyping ofMycoplasma mycoidessubsp.mycoidesSC by multilocus sequence analysis allows molecular epidemiology of contagious bovine pleuropneumonia

“…This typing scheme has been applied successfully to a wide variety of bacterial pathogens such as Staphylococcus aureus [14], Campylobacter jejuni [12], and Haemophilus influenzae [26], to cite only a few. This approach has multiple applications such as phylogeny [18], molecular structure analysis [42], and molecular epidemiology. In molecular epidemiology, MLST can be used to study the evolution of antibiotic resistant strains [17], the temporal trends in strain expansion [29], or the distribution of strains of various lineages within a population [20].…”

Proposed minimal standards for describing new taxa of aerobic, endospore-forming bacteria

“…Wang et al (2007a, b) included gyrB sequence comparisons in studies of the B. subtilis group and demonstrated the synonymy of Bacillus axarquiensis and Bacillus malacitensis with Bacillus mojavensis, and Cerritos et al (2008) included recA sequence comparisons in the work that led to the proposal of Bacillus coalhuilensis. Priest et al (2004), Sorokin et al (2006) and Tourasse et al (2006) used multilocus sequence typing (MLST) of housekeeping genes to investigate population structures within the B. cereus group. It is to be expected that multilocus sequence analysis (MLSA) and MLST schemes will become available through publicly accessible databases.…”

Genomic characterization of theBacillus cereussensu lato species: Backdrop to the evolution ofBacillus anthracis

“…However, although Bacillus is a very diverse genus with more than a hundred species, only the Bacillus cereus group of species is associated with nonopportunistic infections of mammals. This group, comprising B. cereus, Bacillus thuringiensis, B. anthracis, Bacillus mycoides, Bacillus pseudomycoides, and Bacillus weihenstephanensis, is referred to as B. cereus sensu lato (s.l., meaning ''in the widest sense'') (Helgason et al 2000;Jensen et al 2003;Tourasse et al 2006). Despite the multiple species names, which are often attributed to phenotypes conferred by mobile genetic elements, all these organisms can be considered members of a single species, because of their low genetic diversity, as measured by 16S sequencing (Daffonchio et al 2003) and multilocus sequence typing (MLST) (Priest et al 2004), and their high degree of shared gene content (Rasko et al 2005).…”