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Proc Natl Acad Sci U S A. 2013 Aug 13;110(33):13600-5. doi: 10.1073/pnas.1306390110. Epub 2013 Jul 31.

BslA is a self-assembling bacterial hydrophobin that coats the Bacillus subtilis biofilm.

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Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.


Biofilms represent the predominant mode of microbial growth in the natural environment. Bacillus subtilis is a ubiquitous Gram-positive soil bacterium that functions as an effective plant growth-promoting agent. The biofilm matrix is composed of an exopolysaccharide and an amyloid fiber-forming protein, TasA, and assembles with the aid of a small secreted protein, BslA. Here we show that natively synthesized and secreted BslA forms surface layers around the biofilm. Biophysical analysis demonstrates that BslA can self-assemble at interfaces, forming an elastic film. Molecular function is revealed from analysis of the crystal structure of BslA, which consists of an Ig-type fold with the addition of an unusual, extremely hydrophobic "cap" region. A combination of in vivo biofilm formation and in vitro biophysical analysis demonstrates that the central hydrophobic residues of the cap are essential to allow a hydrophobic, nonwetting biofilm to form as they control the surface activity of the BslA protein. The hydrophobic cap exhibits physiochemical properties remarkably similar to the hydrophobic surface found in fungal hydrophobins; thus, BslA is a structurally defined bacterial hydrophobin. We suggest that biofilms formed by other species of bacteria may have evolved similar mechanisms to provide protection to the resident bacterial community.


biofilm hydrophobicity; biofilm surface protein; in situ immunofluorescence

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