Macroscopic amyloid fiber formation by staphylococcal biofilm associated SuhB protein

•Staphylococcal SuhB protein has intrinsic amyloid fiber forming ability.•Overexpression of SaSuhB in E. coli produces extracellular amyloid fibers.•Structural characterization and factors affect in vitro SaSuhB fiber formation.•SaSuhB macro-fiber has a multilayered sheet like morphology.•Multilayered structure facilitates adhering and encasing of bacterial cells.

Staphylococcus aureus is a commensal and opportunistic pathogen that causes lethal infections. Biofilm forming ability of S. aureus enhances its virulence since biofilm provides the bacteria protective shield against antibiotics and host immunity. Polysaccharide independent biofilm formation by several virulent S. aureus strains have been identified recently, where protein components substitute polysaccharide intercellular adhesin (PIA) involved in bacterial cell attachment. The suhB gene has been reported to be essential in staphylococcal PIA-independent biofilm formation. Overexpression of staphylococcal SuhB (SasuhB) in E. coli produces extracellular macroscopic fibers made of recombinant SaSuhB protein. The amyloidic nature of the fiber is evaluated by high resolution electron microscopy, X-ray fiber diffraction and amyloid specific dyes, such as Congo red and thioflavin-T binding assay. The fibers appear to be sticky in nature and bind a large number of bacterial cells. The results suggest the possible role of SaSuhB-fibers as a structural component as well as an adhesin in biofilm matrix.

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