Five strains of phase I were grown in conventional casamino-acid medium and in media modified by adding high concentrations of MgSC>4 or nicotinic acid. Cells grown in high-magnesium media (in the C-mode) had only about 4% of the protective antigen (PA) and 6% of the histamine-sensitising factor (HSF) of cells from the normal medium. Envelopes from C-mode organisms when examined by SDS-PAGE showed a loss of 28k and 30k polypetide bands. Similar parallel losses of PA, HSF and 28k and 30k bands were found with cells from the high-nicotinic-acid medium. A medium with a high concentration of nicotinamide gave cells with normal amounts of PA, HSF and 28k and 30k bands. Growth in high concentrations of NaS0 caused partial losses of PA, HSF and 28k and 30k bands, while a high-succinate medium gave cells with somewhat diminished PA and HSF but without appreciable attenuation of the 28k and 30k bands.

Because of the close correlation between the presence or absence of PA, HSF and 28k and 30k envelope polypeptides, it is suggested that the latter may represent or be closely associated with the components responsible for PA and HSF activities.


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