Paracrystalline layers ( S-layers) sAM易 Many prokaryotes contain a cell surface layer composed of a two-dimensional array of protein called s-layer S-layer has been detected in representatives of virtually every phylogenetic grouping of bacteria and nearly universal among archaea. In some species of Archaea, the s-layer is also the cell wallParacrystalline layers (S-layers) • Many prokaryotes contain a cell surface layer composed of a two-dimensional array of protein called S-layer. • S-layer has been detected in representatives of virtually every phylogenetic grouping of bacteria and nearly universal among Archaea. • In some species of Archaea, the S-layer is also the cell wall