Studies on Immunity in Anthrax XII. Requirement for Phosphate for Elaboration of Protective Antigen and Its Partial Replacement by Charcoal.

Retention of protective antigen on columns of diethylaminoethyl cellulose was inhibited by the 0.01 m phosphate salts in the standard growth medium. Reduction in the concentration of phosphate to 0.001 m allowed satisfactory retention of antigen on diethylaminoethyl cellulose but decreased significantly the elaboration of antigen during growth of the cultures. Growth remained normal at phosphate concentrations as low as 0.0001 m. Inhibition of antigen elaboration in media containing reduced concentrations of phosphate was overcome by addition of 0.006% (w/v) charcoal. It is suggested that antigen elaboration, like encapsulation of virulent strains, is stimulated in the presence of an adsorbent. However, a nonencapsulated strain derived from an F mutant exhibited the same requirement for an adsorbent as nonencapsulated strains derived from the parent strain.