Genomic and pangenomic analysis of Bacillus thuringiensis MH778713, formerly Bacillus cereus, a multi-heavy metal tolerant bacterium

The Bacillus cereus group comprises several Gram-positive, spore-forming bacteria that are widespread in natural environments and exhibit varying degrees of pathogenic potential and industrial relevance. Species-level taxonomic classification of B. cereus group strains remains challenging. Phylogenetic analysis of housekeeping gene sequences is often employed to assign B. cereus group strains to the species level. Still, it is insufficient for accurate taxonomic classification on a genomic scale. Bacillus cereus MH778713 was described as a chromium hyper-tolerant strain, isolated from mesquite shrubs ( Prosopis laevigata ) in Mexico, and described as belonging to the B. cereus species by 16S rDNA and rpo B gene sequence analysis. Long-read genomic sequencing was conducted for Bacillus cereus MH778713, resulting in a high-quality, near-chromosome-level genome with an assembly length of 5.9 Mbp. An Average Nucleotide Identity (ANI) analysis showed that this strain belonged to the Bacillus thuringiensis species, reclassifying this microorganism as B. thuringiensis MH778713. Gene cluster families possibly related to heavy metal tolerance, such as antibiotic resistance, virulence factors, drug targets, and transporters, were found; no plasmids are carried by this strain. A pangenomic analysis of different bacterial species genomes allowed us to identify gene cluster families unique to this strain, possibly related to chromium hyper-tolerance.