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Population structure and evolution of the Bacillus cereus group
Fergus G Priest1, Margaret Barker, Les W J Baillie
1School of Life Sciences, Heriot Watt University, Edinburgh EH14 4AS, UK. f.g.priest@hw.ac.uk
Journal of Bacteriology
|November 18, 2004
Summary
The Bacillus cereus group exhibits a clonal population structure, with distinct lineages identified through multilocus sequence typing. This genetic analysis reveals relationships between Bacillus anthracis, Bacillus cereus, and Bacillus thuringiensis strains.
Area of Science:
- Microbiology
- Genomics
- Bacterial Taxonomy
Background:
- The Bacillus cereus group comprises several species, including important human and animal pathogens, as well as insecticidal strains.
- Understanding the genetic relatedness and population structure of these bacteria is crucial for accurate identification and control.
Purpose of the Study:
- To genetically characterize representative strains of the Bacillus cereus group using multilocus sequence typing (MLST).
- To elucidate the population structure and evolutionary relationships among Bacillus anthracis, Bacillus cereus, Bacillus thuringiensis, and related species.
Main Methods:
- Multilocus sequence typing (MLST) was performed on seven housekeeping genes (glpF, gmk, ilvD, pta, pur, pycA, tpi).
- Phylogenetic analysis, including maximum likelihood (ML) trees and split decomposition, was used to infer population structure and relationships.
- Sequence types (STs) were assigned, and lineages were defined based on genetic divergence.
Main Results:
- Fifty-nine distinct sequence types (STs) were identified among the analyzed Bacillus cereus group strains.
- The population exhibited a generally clonal structure, with two major phylogenetic clades largely separating Bacillus anthracis and Bacillus cereus from the majority of Bacillus thuringiensis strains.
- Eight distinct lineages were defined within the major clades, with some Bacillus thuringiensis serovars showing high genetic homogeneity (e.g., aizawai, kenyae, tolworthi) while others were heterogeneous (e.g., canadensis).
Conclusions:
- The study confirms a clonal population structure within the Bacillus cereus group, supporting the use of MLST for strain differentiation.
- The identified lineages provide a framework for understanding the evolutionary history and relationships among these important bacterial species.
- A revision of nomenclature is proposed to better reflect the clonal structure and genetic lineages, integrating lineage and clone designations with STs.