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J. Bacteriol., Jul 1997, 4493-4500, Vol 179, No. 14
AA Al Mamun, A Tominaga and M Enomoto
To detect genetic defects that might have caused loss of flagella in
Shigella boydii and Shigella sonnei, the region III flagellar (fli) operons
were cloned from certain strains and analyzed with reference to the
restriction maps and genetic maps of Escherichia coli fli operons. S.
boydii NCTC9733 (strain C5 in this paper) had the 988-bp internal deletion
in the fliF gene that encodes a large substructural protein of the basal
body. Two strains (C1 and C8) had deletions of the entire fliF operon, and
the remaining three (C3, C4, and C9) differed in the size of the
restriction fragments carrying the fliF and fliL operons. Loss of flagella
in S. boydii appears to originate in some defect in the fliF operon. S.
sonnei IID969 lacked the fliD gene and, in place of it, carried two IS600
elements as inverted repeats. Genes downstream from fliD were not detected
in the cloned fragment despite its large size but did appear elsewhere in
the chromosome. The fliD gene encodes a cap protein of the flagellar
filament, and its deletion results in overexpression of class 3 operons by
the increased amount of FliA (sigmaF) caused by the excess export of the
anti-sigma factor FlgM. Three other strains also had the fliD deletion, and
two of them had another deletion in the fliF-fliG-fliH region. The fliD
deletion might be the primary cause of loss of flagella in S. sonnei. The
lack of FliF or FliD in each subgroup is discussed in connection with the
maintenance of virulence and bacterial growth. We also discuss the process
of loss of flagella in relation to transposition of IS elements and
alterations of the noncoding region, which were found to be common to at
least three subgroups.
Copyright © 1997, American Society for Microbiology
Cloning and characterization of the region III flagellar operons of the four Shigella subgroups: genetic defects that cause loss of flagella of Shigella boydii and Shigella sonnei
Department of Biology, Faculty of Science, Okayama University, Japan.
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