title: BslA is a self-assembling bacterial hydrophobin that coats the Bacillus subtilis biofilm.
abstract: 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.
authors.affiliation: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.
authors.forename: Laura
authors.initials: L
authors.lastname: Hobley
authors.forename: Adam
authors.initials: A
authors.lastname: Ostrowski
authors.forename: Francesco V
authors.initials: FV
authors.lastname: Rao
authors.forename: Keith M
authors.initials: KM
authors.lastname: Bromley
authors.forename: Michael
authors.initials: M
authors.lastname: Porter
authors.forename: Alan R
authors.initials: AR
authors.lastname: Prescott
authors.forename: Cait E
authors.initials: CE
authors.lastname: MacPhee
authors.forename: Daan M F
authors.initials: DM
authors.lastname: van Aalten
authors.forename: Nicola R
authors.initials: NR
authors.lastname: Stanley-Wall
mesh_terms: D001412:Bacillus subtilis / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018441:Biofilms; D001703:Biophysics; D005455:Fluorescent Antibody Technique; D057927:Hydrophobic and Hydrophilic Interactions; D018613:Microscopy, Confocal; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D001426:Bacterial Proteins
keywords: biofilm hydrophobicity; biofilm surface protein; in situ immunofluorescence
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