Scientific Publications
The type F6 neurotoxin gene cluster locus of Group II Clostridium botulinum has evolved by successive disruption of two different ancestral precursors
Genome Biology and Evolution, 5, 1032-1037
Genome sequences of five different Group II (non-proteolytic) Clostridium botulinum type F6 strains were compared at a 50 kb locus containing the neurotoxin gene cluster. A clonal origin for these strains is indicated by the fact that sequences were identical except for strain Eklund 202F, with 10 SNPs and a 15bp deletion. The essential topB gene encoding topoisomerase III was found to have been split by the apparent insertion of 34.4 kb of foreign DNA (in a similar manner to that in Group II C. botulinum type E where the rarA gene has been disrupted by a neurotoxin gene cluster). The foreign DNA, which includes the intact 13.6 kb type F6 neurotoxin gene cluster, bears not only a newly introduced topB gene, but also two non-functional remnants of a type B and a type E botulinum neurotoxin gene. This observation, combined with the discovery of bacteriophage integrase genes and IS4 elements suggest that several rounds of recombination/horizontal gene transfer have occurred at this locus. The simplest explanation for the current genotype is that the ancestral bacterium, a Group II C. botulinum type B strain, received DNA firstly from a strain containing a type E neurotoxin cluster, then from a strain containing a type F6 neurotoxin gene cluster. Each event disrupted the previously functional neurotoxin gene. This degree of successive recombination at one hot-spot is without precedent in C. botulinum, and it is also the first description of a Group II C. botulinum genome containing more than one neurotoxin gene sequence.
Genome Biology and Evolution, 5, 1032-1037
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