Aggregation mechanism of the protein TasA in acidic conditions

Biofilms are multicellular bacterial communities held together by a self-produced extracellular matrix (ECM) that form on surfaces and interfaces. The ECM is principally composed by proteins, polysaccharides and nucleic acids. This matrix confers resistance and protection to both antimicrobials and host defences. In our laboratory, we use the nonpathogenic Gram-positive bacterium Bacillus subtilis as a model for biofilm formation. One of the principal proteins in the B. subtilis biofilm is an amyloid like protein, TasA. This protein aggregates at around pH 2.5. To understand the aggregation mechanism, aggregates of TasA were prepared in the presence of gold nanoparticles with positive, negative and neutral functionalities. In addition, measurements of the Zeta-potential of the protein as a function of pH were done. The results suggest that the mechanism is similar to a colloidal aggregation model. Finally, Static light scattering measurements of the protein aggregate were performed, from which a fractal dimension of 2.2 was calculated, corresponding to a reaction limited aggregation. Understanding the aggregation mechanism could lead to the creation of TasA aggregation inhibitors that may also affect the biofilm growth.