Comparison of assembled Clostridium botulinum A1 genomes revealed their evolutionary relationship

Clostridium botulinum encompasses bacteria that produce at least one of the seven serotypes of botulinum neurotoxin (BoNT/A-G). The availability of genome sequences of four closely related Type A1 or A1(B) strains, as well as the A1-specific microarray, allowed the analysis of their genomic organizations and evolutionary relationship. The four genomes share > 90% core genes and > 96% functional groups. Phylogenetic analysis based on COG shows closer relations of the A1(B) strain, NCTC 2916, to B1 and F1 than A1 strains. Alignment of the genomes of the three A1 strains revealed a highly similar chromosomal structure with three small gaps in the genome of ATCC 19397 and one additional gap in the genome of Hall A, suggesting ATCC 19379 as an evolutionary intermediate between Hall A and ATCC 3502. Analyses of the four gap regions indicated potential horizontal gene transfer and recombination events important for the evolution of A1 strains.