The study sequences and analyzes the genome of *Bacillus cereus* ATCC 14579, comparing it with the gapped genome of *Bacillus anthracis* A2012. The analysis aims to identify conserved and unique genes between the two species, clarifying their phylogenetic relationship and species-specific markers. Key findings include: 1. **Genome Structure**: The *B. cereus* ATCC 14579 genome shows regions with varying G+C content, suggesting phage-mediated recombination. A linear plasmid, pBclin15, is identified, which may have originated from a phage. 2. **Phylogenetic Analysis**: Despite close ecological niches, *B. cereus* and *B. anthracis* are not closely related. However, 4,505 coding sequences (CDSs) in *B. cereus* have high identity (80-100%) to their homologues in *B. anthracis*, with an average identity of 92.1%. 3. **Core Genes**: A large core set of genes (75-80%) is conserved between *B. cereus* and *B. anthracis*, indicating a common ancestor. These genes suggest that the *cereus* group ancestor was not a soil bacterium but an opportunistic insect pathogen. 4. **Pathogenicity Genes**: Surprisingly, *B. cereus* ATCC 14579 contains genes for toxins and other pathogenicity factors, unlike many clinical isolates. This suggests that the *cereus* group ancestor was an opportunistic insect pathogen. 5. **Regulatory Networks**: The pleiotropic regulator PlcR plays a crucial role in *B. cereus* virulence, with multiple binding sites identified. The presence of PlcR paralogues and a histidine protein kinase homologous to the sporulation kinase KinB indicate a complex regulatory network. 6. **Unique Genes**: Approximately 15% of the CDSs are unique to each species. Unique genes include a cluster for capsular polysaccharide biosynthesis in *B. cereus* and a cluster for teichoic acid or secondary cell wall polymer biosynthesis in *B. anthracis*. 7. **Genome Comparison**: The availability of both complete and gapped genome sequences allows for detailed phylogenetic analysis and the identification of genes crucial for host colonization and bacterial propagation. This study provides insights into the genetic diversity and evolution of the *cereus* group, highlighting the distinct and overlapping features of *B. cereus* and *B. anthracis*.The study sequences and analyzes the genome of *Bacillus cereus* ATCC 14579, comparing it with the gapped genome of *Bacillus anthracis* A2012. The analysis aims to identify conserved and unique genes between the two species, clarifying their phylogenetic relationship and species-specific markers. Key findings include: 1. **Genome Structure**: The *B. cereus* ATCC 14579 genome shows regions with varying G+C content, suggesting phage-mediated recombination. A linear plasmid, pBclin15, is identified, which may have originated from a phage. 2. **Phylogenetic Analysis**: Despite close ecological niches, *B. cereus* and *B. anthracis* are not closely related. However, 4,505 coding sequences (CDSs) in *B. cereus* have high identity (80-100%) to their homologues in *B. anthracis*, with an average identity of 92.1%. 3. **Core Genes**: A large core set of genes (75-80%) is conserved between *B. cereus* and *B. anthracis*, indicating a common ancestor. These genes suggest that the *cereus* group ancestor was not a soil bacterium but an opportunistic insect pathogen. 4. **Pathogenicity Genes**: Surprisingly, *B. cereus* ATCC 14579 contains genes for toxins and other pathogenicity factors, unlike many clinical isolates. This suggests that the *cereus* group ancestor was an opportunistic insect pathogen. 5. **Regulatory Networks**: The pleiotropic regulator PlcR plays a crucial role in *B. cereus* virulence, with multiple binding sites identified. The presence of PlcR paralogues and a histidine protein kinase homologous to the sporulation kinase KinB indicate a complex regulatory network. 6. **Unique Genes**: Approximately 15% of the CDSs are unique to each species. Unique genes include a cluster for capsular polysaccharide biosynthesis in *B. cereus* and a cluster for teichoic acid or secondary cell wall polymer biosynthesis in *B. anthracis*. 7. **Genome Comparison**: The availability of both complete and gapped genome sequences allows for detailed phylogenetic analysis and the identification of genes crucial for host colonization and bacterial propagation. This study provides insights into the genetic diversity and evolution of the *cereus* group, highlighting the distinct and overlapping features of *B. cereus* and *B. anthracis*.