Effect of the lower molecular capsule released from the cell surface of Bacillus anthracis on the pathogenesis of anthrax

Bacillus anthracis enters the body as an endospore, and encapsulation and toxin production occur after germination. Capsule is proposed to be an antiphagocytic factor, and toxin induces cytokine production for systemic shock. The dep gene, adjacent to the cap region for the encapsulation, degrades the high-molecular weight capsule (H-capsule) to the lower-molecular weight capsule (L-capsule), which releases into the culture supernatant. This study analyzed the biological function of the cap-dep region. The dep null mutant Sm-1, which formed H-capsule but not L-capsule, was avirulent. However, Sm-1 with an intact dep gene or with purified L-capsule recovered its pathogenicity. Sm-1 was subjected to phagocytosis by macrophages more easily than its parent strain, Sm, in vitro; in vivo, it cleared without L-capsule and grew well with L-capsule, which suggests that L-capsule is essential for in vivo multiplication. Moreover, a new name, capD, might be appropriate, because of the part of the cap operon involved in both polymerization and depolymerization of the capsule.