Amyloid fibers provide structural integrity to Bacillus subtilis biofilms

Abstract

Bacillus subtilis forms biofilms whose constituent cells are held together by an extracellular matrix. Previous studies have shown that the protein TasA and an exopolysaccharide are the main components of the matrix. Given the importance of TasA in biofilm formation, we characterized the physicochemical properties of this protein. We report that purified TasA forms fibers of variable length and 10–15 nm in width. Biochemical analyses, in combination with the use of specific dyes and microscopic analyses, indicate that TasA forms amyloid fibers. Consistent with this hypothesis, TasA fibers required harsh treatments (e.g., formic acid) to be depolymerized. When added to a culture of a tasA mutant, purified TasA restored wild-type biofilm morphology, indicating that the purified protein retained biological activity. We propose that TasA forms amyloid fibers that bind cells together in the biofilm.

Atomic force microscopy – looking at mechanosensors on the cell surface

“…Hence, the strength of yeast cell-cell adhesion results from the force-induced amyloid-like clustering of hundreds of proteins on the cell surface to form arrays of ordered multimeric binding sites (Lipke et al, 2012). These results highlight the role that functional amyloids can have in cell adhesion, both in lateral clustering (in cis) of many adhesion proteins to increase binding avidity, and in the potential to form stable amyloid-type bonds between cells (in trans), a mechanism that we expect to be detected in many more organisms as more cell adhesion systems are examined (Romero et al, 2010). Interestingly, the above mechanical restructuring is reminiscent of shear-induced unfolding and refolding of proteins during blood clotting, where force induces the exposure of interaction sites in the blood glycoprotein von Willebrand factor (VWF), which has recently been demonstrated by single-molecule laser tweezer experiments (Kim et al, 2010).…”

Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis

“…In addition, harpintreated Arabidopsis plants also showed down-regulation of important plant defense genes such as WRKY transcription factors and oxidative burst-associated genes like NADPH oxidases (Livaja et al, 2008). B. subtilis has recently been shown to produce amyloid fibers that were important to regulate the structural integrity in B. subtilis biofilms (Romero et al, 2010). To our knowledge, other than harpins, no other amyloid fibers have been reported to interact with plants.…”

Evolution of exploitative interactions during diversification in Bacillus subtilis biofilms

“…S1A). Inspired by the striking difference in appearance of the morphotypes on LB medium, we introduced the following names: Wrinkly -displaying an increased complexity in the colony center; Rough -similar to the ancestor; Spreader -showing dramatically increased colony expansion; and Smooth -exhibiting a very flat surface similar to certain biofilm mutants (Romero et al 2010) (Fig. 1B).…”