SUMMARY: A curly flagellar mutant obtained from a strain of was unstable and repeatedly dissociated ‘curly’ and normal subclones. Examination of flagellar antigens of the normal and the curly flagellar subclones demonstrated that the changes in flagellar shape corresponded exactly with phase variation: subclones with curly flagella were always in phase-1 (antigen-), those with normal flagella were in phase-2 (antigen-). In transduction from a normal flagellar strain to the curly phase-1 strain, transductional clones with normal flagella were isolated. The transductional clones showed the antigen of the donor in phase-1 and that of the recipient in phase-2. This indicates that the phase-1 curly determinant is closely associated with the phase-1 antigen type determinant, .

Seven curly mutants were obtained from a strain of : one with antigen- (phase-1), and four with antigen- (phase-2), and two with antigen- (phase-2) from a transductional recombinant given antigen-. Transductional analysis with these strains showed that the phase-2 curly determinant is closely associated with the phase-2 antigen type determinant, ; and the phase-1 curly determinant with . In cross-absorption experiments with antisera prepared against flagella of either normal or curly mutant, no antigenic difference between normal and curly flagella could be detected. It is inferred that and are the primary structural determinants of flagellar protein in phase-1 and phase-2 respectively; mutation in or may cause an altered configuration of flagellar protein, resulting in a change in antigenic type, or in flagellar shape, or it may cause the failure of flagellar morphogenesis. Attempts to obtain recombination by transduction between the curly flagellar determinants in each of the phases have beeen unsuccessful; this suggests that in each phase the mutant sites of the curly types are very closely linked or identical.


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