Studies on immunity in anthrax. IV. Factors influencing elaboration of the protective antigen of Bacillus anthracis in chemically defined media

Elaboration of the protective antigen of Bacillus anthracis in a chemically defined, nonprotein medium was described in a previous report from these laboratories (Wright et al., 1954). This medium, referred to as 528 medium, was composed of 17 amino acids, glutamine, adenine, guanine, uracil, thiamin, glucose, sodium bicarbonate, and inorganic salts. Sterile filtrates of cultures of B. anthracis in the medium produced effective immunity in rabbits, guinea pigs, and monkeys; the dose required to induce significant immunity in rabbits was of the same order as that of the edema fluid of anthrax lesions (Cromartie et al., 1947). Certain minor modifications in the composition of the medium markedly influenced the antigenic potency, suggesting that elaboration of antigen is asso-ciated with a particular type of metabolic activity of the organism. Further knowledge of the conditions for elaboration of antigen was desirable to facilitate production of antigen on a practical scale, to indicate the general relationship of antigen elaboration to growth of the organism, and to provide information desirable for investigating the existence and significance of extracellular antigens of this general type in other organisms. Certain relationships of constituents of the medium and conditions of growth to accumula-tion of protective antigen were therefore investi-gated in greater detail; considerable simplification and improvement of the medium and cultural conditions were found to be possible. The results suggest certain preliminary inferences regarding the metabolic processes associated with elaboration of antigen. MATERIALS AND METHODS Cultures. A standard spore suspension of the Vollum strain of B. anthracis was use