MUTATIONS IN THE RFBT GENE ARE RESPONSIBLE FOR THE OGAWA TO INABA SEROTYPE CONVERSION IN VIBRIO-CHOLERAE-01

In cultures of Vibrio cholerae strains of Ogawa serotype, variant stra ins which had undergone serotype conversion from Ogawa to Inaba were i dentified. The rfbT genes cloned from the parent strains were found to produce a 31-kDa protein in the maxicell system, and to cause serotyp e conversion when introduced into E. coli cells expressing Inaba serot ype specificity. On the other hand, rfbT genes cloned from the variant strains neither produced the 31-kDa protein nor caused serotype conve rsion. Nucleotide sequence of these rfbT genes as well as those of two clinical Vibrio cholerae strains of Inaba serotype revealed that muta tions causing premature termination of their rfbT genes were invariabl y present in strains expressing Inaba serotype specificity. The result strongly suggested that genetic alteration of the rfbT gene is respon sible for serotype conversion of Vibrio cholerae O1.