An evolutionary analysis of nitric oxide reductase gene norV in enterohemorrhagic Escherichia coli O157

- We examined that the deletion of norV gene in EHEC O157 evolutionarily occurred at a point between cluster 1 and cluster 2.
- All intact-norV-type EHEC O157 were resistant to nitric oxide stress under anaerobic conditions.
- Genetic change in norV in EHEC O157 was a stable marker of transition from cluster 1 to cluster 2.

A novel virulence gene, norV, that encodes nitric oxide (NO) reductase, was examined to investigate the emergence of enterohemorrhagic Escherichia coli (EHEC) O157 subgroup C clusters 2 and 3 from subgroup C cluster 1. Deletion of norV occurred at a point between cluster 1 and cluster 2 just after or at the same time that an stx2 bacteriophage, which retains Shiga toxin 2 gene, was inserted into wrbA, which encodes a novel multimeric flavodoxin-like protein, in EHEC O157. Sensitivity of NO to anaerobic growth was correlated with the deletion of norV in all EHEC O157 individuals tested. The C467A mutation of fimH, which encodes minor component of type 1 fimbriae, occurred within cluster 1, not as a transition from cluster 1 to cluster 2, indicating that there is a cluster 1 minority branch that leads to cluster 2. These data refine the evolutionary history of an emerging EHEC O157.