THE CAPSULE AND S-LAYER - 2 INDEPENDENT AND YET COMPATIBLE MACROMOLECULAR STRUCTURES IN BACILLUS-ANTHRACIS

Bacillus anthracis, the etiological agent of anthrax, is a gram-positi ve spore-forming bacterium, Fully virulent bacilli are toxinogenic and capsulated, Two abundant surface proteins, including the major antige n, are components of the B. anthracis surface layer (S-layer). The B. anthracis paracrystalline S-layer has previously only been found in no ncapsulated vegetative cells. acre we report that the S-layer proteins are also synthesized under conditions where the poly-gamma-D-glutamic acid capsule is present, Structural and immunological analyses show t hat the capsule is exterior to and completely covers the S-layer prote ins, Nevertheless, analysis of single and double S-layer protein mutan ts shows that the presence of these proteins is not required far norma l capsulation of the bacilli, Similarly, the S-layer proteins assemble as a two-dimensional crystal, even in the presence of the capsule. Th us, both structures are compatible, and yet neither is required for th e correct formation of the other.