FLAGELLIN-CONTAINING MEMBRANE-VESICLES EXCRETED FROM VIBRIO-ALGINOLYTICUS MUTANTS LACKING A POLAR-FLAGELLAR FILAMENT

Polar flagellum-defective mutants (Pof(-) Laf(-)) have been isolated f rom a lateral flagella-defective mutant (Pof(+) Laf(-)). Among these P of(-) Laf(-) mutants, polar-filamentless mutants, which have the hook structure but not the filament, were identified by electron microscopy , Their hooks were covered with a sheath structure which is contiguous to the outer membrane, The filament proteins, flagellins, were shed i nto the culture medium of these mutants. These flagellins could be sed imented by high-speed centrifugation even after heat or low pH treatme nt whereas the depolymerized flagellin of the Pof(+) strain was degrad ed by these treatments. After Triton X-100 treatment, most flagellin o f the filamentless mutants could no longer be sedimented, and was degr aded. We observed vesicle-like structures on the tips of the hooks and in the flagellin fraction sedimented by high speed centrifugation, Th ese results suggest that flagellin of the filamentless mutants is not assembled into the tip of the hook, but is excreted together with a me mbrane structure which is probably the sheath of polar flagella.