Loss of Bacitracin Resistance Due to a Large Genomic Deletion amongBacillus anthracisStrains

ABSTRACTBacillus anthracisis a Gram-positive endospore-forming bacterial species that causes anthrax in both humans and animals. In Zambia, anthrax cases are frequently reported in both livestock and wildlife, with occasional transmission to humans, causing serious public health problems in the country. To understand the genetic diversity ofB. anthracisstrains in Zambia, we sequenced and compared the genomic DNA ofB. anthracisstrains isolated across the country. Single nucleotide polymorphisms clustered these strains into three groups. Genome sequence comparisons revealed a large deletion in strains belonging to one of the groups, possibly due to unequal crossing over between a pair of rRNA operons. The deleted genomic region included genes conferring resistance to bacitracin, and the strains with the deletion were confirmed with loss of bacitracin resistance. Similar deletions between rRNA operons were also observed in a fewB. anthracisstrains phylogenetically distant from Zambian strains. The structure of bacitracin resistance genes flanked by rRNA operons was conserved only in members of theBacillus cereusgroup. The diversity and genomic characteristics ofB. anthracisstrains determined in this study would help in the development of genetic markers and treatment of anthrax in Zambia.IMPORTANCEAnthrax is caused byBacillus anthracis, an endospore-forming soil bacterium. The genetic diversity ofB. anthracisis known to be low compared with that ofBacillusspecies. In this study, we performed whole-genome sequencing of Zambian isolates ofB. anthracisto understand the genetic diversity between closely related strains. Comparison of genomic sequences revealed that closely related strains were separated into three groups based on single nucleotide polymorphisms distributed throughout the genome. A large genomic deletion was detected in the region containing a bacitracin resistance gene cluster flanked by rRNA operons, resulting in the loss of bacitracin resistance. The structure of the deleted region, which was also conserved among species of theBacillus cereusgroup, has the potential for both deletion and amplification and thus might be enabling the species to flexibly control the level of bacitracin resistance for adaptive evolution.