Abstract
The Gram-negative oral pathogen Tannerella forsythia is decorated with a 2D crystalline surface (S-) layer, with two different S-layer glycoprotein species being present. Prompted by the predicted virulence potential of the S-layer, this study focused on the analysis of the arrangement of the individual S-layer glycoproteins by a combination of microscopic, genetic, and biochemical analyses. The two S-layer genes are transcribed into mRNA and expressed into protein in equal amounts. The S-layer was investigated on intact bacterial cells by transmission electron microscopy, by immune fluorescence microscopy, and by atomic force microscopy. The analyses of wild-type cells revealed a distinct square S-layer lattice with an overall lattice constant of 10.1 ± 0.7 nm. In contrast, a blurred lattice with a lattice constant of 9.0 nm was found on S-layer single-mutant cells. This together with in vitro self-assembly studies using purified (glyco)protein species 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 T. forsythia cells, which might impact the pathogenicity of this bacterium.
Highlights
The periodontal pockets of humans harbor more than 500 bacterial species
(Fig. 1a) and periodic acid-SchiV (PAS) staining for carbohydrates (Posch et al 2011), with these S-layer glycoproteins corresponding together to approximately 10% of whole cellular protein according to intensity signal integration
The disease progresses as a result of the direct eVects of bacterial virulence factors on host tissues, as well as self-damaging host responses to the colonizing bacteria (Socransky et al 1998)
Summary
The periodontal pockets of humans harbor more than 500 bacterial species. Among them is a group of bacteria that constitute the “red complex”, comprising Tannerella forsythia, Porphyromonas gingivalis, and Treponema denticola, with the latter being strongly implicated in the onset of periodontitis (Socransky et al 1998). Periodontitis is a chronic inXammation of the periodontium with multifactorial etiology. Tannerella forsythia is an anaerobic Gram-negative bacterium belonging to the Cytophaga-Bacteroidetes-Firmicutes cluster of bacteria. It was initially named Bacteroides forsythus (Tanner et al 1986) and later reclassiWed as T. forsythia (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
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