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J. Bacteriol., 07 1996, 3722-3726, Vol 178, No. 13
AA Al Mamun, A Tominaga and M Enomoto
Strains in the genus Shigella are nonmotile, but they retain some cryptic
flagellar operons whether functional or defective (A.Tominaga, M. A.-H.
Mahmoud, T. Mukaihara, and M. Enomoto, Mol. Microbiol. 12:277- 285, 1994).
To disclose the cause of motility loss in shigellae, the presence or
defectiveness of the flhD and flhC genes, composing the master operon whose
mutation causes inactivation of the entire flagellar regulon, was examined
in the four Shigella subgroups. The flhD operon cloned from Shigella boydii
and Shigella sonnei can activate, though insufficiently, the regulon in the
Escherichia coli flhD or flhC mutant background. The clone from Shigella
dysenteriae has a functional flhD gene and nonfunctional flhC gene, and its
inactivation has been caused by the IS1 element inserted in its 5' end. The
operon of Shigella flexneri is nonfunctional and has suffered an
IS1-insertion mutation at the 5' end of the flhD gene. Comparison of
restriction maps indicates that only the central 1.8-kb region, including
part of the flhC gene and its adjacent mot operon, is conserved among the
four Shigella subgroups as well as in E. coli, but in Salmonella
typhimurium the whole map is quite different from the others. Motility loss
in shigellae is not attributable to genetic damage in the master operon of
a common ancestor, but it occurs separately in respective ancestors of the
four subgroups, and in both S. dysenteriae and S.flexneri IS1 insertion in
the master operon might be the primary cause of motility loss.
Copyright © 1996, American Society for Microbiology
Detection and characterization of the flagellar master operon in the four Shigella subgroups
Department of Biology, Faculty of Science, Okayama University, Japan.
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