The Gram-negative oral pathogen is furnished using a 2D crystalline surface area (S-) layer, with two different S-layer glycoprotein species being present. 9.0?nm was entirely on S-layer single-mutant cells. This as well as in vitro self-assembly research using purified (glyco)proteins types indicated their increased structural flexibility after self-assembly and/or impaired self-assembly capability. In conjunction with TEM analyses of thin-sectioned cells, this study demonstrates the unusual case that two S-layer glycoproteins are co-assembled into a single S-layer. Additionally, flagella and pilus-like structures were observed on cells, which might impact the pathogenicity of this bacterium. meets the criteria for being considered (+)-JQ1 manufacturer a periodontal pathogen (Socransky 1979) because of (1) its association with and increased levels in periodontitis (Socransky et al. 1998), (2) the evidence of host responses to its antigens (Bird et al. 2001; Yoo et al. 2007), (3) its ability to cause disease in animal models (Sharma et al. 2005; Kesavalu et al. 2007), and (4) the presence of distinct virulence factors that can contribute to the disease process (Sharma 2010). is an anaerobic Gram-negative bacterium belonging to the cluster of bacteria. It was TSPAN33 initially named (Tanner et al. 1986) and later reclassified as (Sakamoto et al. 2002). Its cell surface is covered with a regularly arrayed surface (S-) layer (for review see Messner et al. 2010), and early electron microscopic investigations have shown the presence of an orthogonal S-layer lattice (Kerosuo 1988). SDS-PAGE of intact cells revealed that (+)-JQ1 manufacturer two high-molecular-mass glycoproteins of 230 and 270?kDa are present in and gene, respectively (Higuchi et al. 2000; Lee et al. 2006). The 1,179-amino acid TfsA and the 1,364-amino acid TfsB proteins have a calculated molecular mass of 132 and 154?kDa, respectively, with pI values of 7.8 and 9.9, respectively. Comparison with database entries indicated that this S-layer proteins of apparently have unique sequences exhibiting no homology to other known S-layer proteins of prokaryotic organisms. Only recently, these S-layer proteins were shown to be covalently modified with identical S-layer is not yet known, but there are indications that it might be an important virulence factor (Sakakibara et al. 2007; Sharma 2010; Sekot et al. 2011). These include the demonstration that this S-layer mediates adhesion and/or invasion to human gingival epithelial cells (Sakakibara et al. 2007) as well as its potential to delay the recognition of by the innate immune system of the host (Sekot et al. 2011). This underlines the importance of the bacterial cell surface in conferring to pathogenicity. For analyzing the role of the S-layer proteins in adhesion to and invasion of human gingival epithelial cells, defined insertional inactivation mutants of either of the S-layer genes (named and plays an important role in the initiation stage of oral (+)-JQ1 manufacturer contamination, including periodontal disease (Sakakibara et al. 2007; Sekot et al. 2011). While most S-layer lattices are composed of a single (glyco)protein species (Messner et al. 2010), data from literature indicate that in strain MW5 where two, presumably identical, hexagonal S-layer (+)-JQ1 manufacturer lattices are superimposed (Stewart and Murray 1982). While the underlying layer is attached to the lipopolysaccharide of the outer membrane, the (+)-JQ1 manufacturer second layer appears to be attached directly to the first layer. Whereas in according to the electron microscopy data published by Sakakibara et al(2007). This poses the interesting questions of how the two different S-layer glycoprotein species of are arranged, with the principal options for (1) superimposition of two individually assembled S-layers or (2) co-assembly of the two S-layer glycoproteins into a single S-layer. For building up a defined S-layer ultrastructure, it has to be taken into account that this S-layer proteins are glycosylated (Posch et al. 2011), with glycans naturally occurring in an outward orientation, which would allow them to carry out yet to be identified biological functions. To assess the potential of the cell surface in the bacteriumChost cross talk the understanding of the S-layer ultrastructure as outermost cell envelope component is essential. Therefore, in this study, different microscopic approaches were applied to characterize the native cell surface of wild-type and S-layer mutant cells as well as the self-assembly capability of isolated native S-layer.