The capsule and S-layer:: Two independent and yet compatible macromolecular structures in Bacillus anthracis

Bacillus anthracis, the etiological agent of anthrax, is a gram-positive spore-forming bacterium, Fully virulent bacilli are toxinogenic and capsulated, Two abundant surface proteins, including the major antigen, are components of the B. anthracis surface layer (S-layer). The B. anthracis paracrystalline S-layer has previously only been found in noncapsulated 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 that the capsule is exterior to and completely covers the S-layer proteins, Nevertheless, analysis of single and double S-layer protein mutants shows that the presence of these proteins is not required far normal capsulation of the bacilli, Similarly, the S-layer proteins assemble as a two-dimensional crystal, even in the presence of the capsule. Thus, both structures are compatible, and yet neither is required for the correct formation of the other.