Bacillus anthracis surface: capsule and S-layer

Two abundant surface proteins, EA1 and Sap, are components of the Bacillus anthracis surface layer (S-layer), Their corresponding genes have been clon ed, shown to be clustered on the chromosome and sequenced. EA1 and Sap each possess three 'S-layer homology' motifs. Single and double disrupted mutan ts were constructed. EA1 and Sap Were co-localized at the cell surface of b oth the non-capsulated and capsulated bacilli. When present, the capsule is exterior to, and completely covers, the S-lay er proteins, which form an a rray beneath it. Nevertheless, the presence of these proteins is not requir ed for normal capsulation of the bacilli. Thus both structures are compatib le, and yet neither is required for the correct formation of the other. Bac illus anthracis has, therefore, a very complex cell wall organization for a Gram-positive bacterium.