CLONING AND CHARACTERIZATION OF THE REGION-III FLAGELLAR OPERONS OF THE 4 SHIGELLA SUBGROUPS - GENETIC-DEFECTS THAT CAUSE LOSS OF FLAGELLA OF SHIGELLA-BOYDII AND SHIGELLA-SONNEI

To detect genetic defects that might have caused loss of flagella in S higella boydii and Shigella sonnei, the region III flagellar (fli) ope rons were cloned from certain strains and analyzed,vith reference to t he restriction maps and genetic maps of Escherichia coli fli operons. S. boydii NCTC9733 (strain C5 in this paper) had the 988-bp internal d eletion in the fliF gene that encodes a large substructural protein of the basal body. Two strains (C1 and C8) had deletions of the entire f liF operon, and the remaining three (C3, C4, and C9) differed in the s ize of the restriction fragments carrying the fliF and fliL operons. L oss of flagella in S. boydii appears to originate in some defect in th e fliF operon. S. sonnei IID969 lacked the fliD gene and, in place of it, carried two IS600 elements as inverted repeats. Genes dowstream fr om fliD were not detected in the cloned fragment despite its large siz e but did appear elsewhere in the chromosome. The fliD gene encodes a cap protein of the flagellar filament, and its deletion results in ove rexpression of class 3 operons by the increased amount of FliA (sigma( F)) caused by the excess export of the anti-sigma factor FlgM. Three o ther strains also had the fliD deletion, and two of them had another d eletion in the fliF-fliG-fliH region. The fliD deletion might be the p rimary cause of loss of flagella in S. sonnei. The lack of FliF or Fli D 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 thr ee subgroups.