BackgroundBacillus anthracis is a causal agent of a zoonotic disease relevant for many countries, and is an agent of bioterrorism. Meanwhile, the reasons for the dependence on tryptophan of some strains with altered virulence have not been established with an almost complete absence of information on the tryptophan operon of this pathogen. In this study, we report gene variability and the structure of the tryptophan operon in B. anthracis strains of the three main lineages.ResultsFor in silico analysis we used 112 B. anthracis genomes, including 68 of those available at the GenBank database and 44 sequenced at our institute. The B. anthracis tryptophan operon has an ancestral structure with a complete set of seven partially overlapping genes. The results show that the variability of all seven tryptophan operon genes is determined by the presence of single nucleotide polymorphisms and InDels. The trpA genes of strains of the main lineage B and trpG genes of strains of the C lineage are pseudogenes and the proteomes lack the corresponding enzymes of the biosynthetic pathway, which may explain the dependence of the strains of line B on tryptophan. ConclusionIn this study, the differences in tryptophan operon genes for B. anthracis strains belonging to different main lineages were demonstrated for the first time. Mutation in the gene of the tryptophan synthase subunit alpha can explain the dysfunction of this enzyme and the dependence on tryptophan in strains of the main lineage B. Identified features suggest a further study of the dependence on tryptophan in B. anthracis strains of the main lineage B and may be of interest from the point of view of intraspecific evolution of the anthrax pathogen.