Physicochemical characterization of a thermostable glycoprotein bioemulsifier from Solibacillus silvestris AM1

• Genus Solibacillus has been reported for the first time for bioemulsifier production.
• This is the first report of flagellin-like glycoprotein bioemulsifier.
• Bioemulsifier AM1 is thermostable, salt tolerant and active in wide pH range.
• It is versatile in emulsifying aliphatic and aromatic hydrocarbons as well as oils.
• Emulsions formed by it have pseudoplastic non-Newtonian rheological properties.

A novel estuarine bacterial strain, Solibacillus silvestris AM1, was found to produce an extracellular, multimeric glycoprotein bioemulsifier, termed AM1, with a MW of 200 kDa and containing 30 kDa monomeric subunits. The bioemulsifier contained 3.6% of the minor carbohydrate components galactose and ribose/xylose. LC/MS-MS of the 30 kDa subunit revealed its homology with a flagellin-like protein arranged in the form of fibers, as shown by transmission electron micrographs. This is the first report of a flagellin-like protein that exhibits bioemulsifier activity being produced from a member of the Solibacillus genus. Bioemulsifier AM1 has a high emulsification index of 62.5% with 10−2 critical micellar dilution. It was found to be thermostable and active in the pH 5–9 and 0–5 M NaCl ranges. Moreover, AM1 formed stable emulsions with a broad range of solvents, including aliphatics, aromatic hydrocarbons and oils, performing better than the well-known bioemulsifier emulsan. Emulsions formed with trichlorobenzene and paraffin oil have a pseudoplastic non-Newtonian rheological property, as observed by particle size and shear stress analysis. AM1, an eco-friendly bioemulsifier, formed stable emulsions in varied physical conditions, and these attributes may prove to be advantageous in cosmetic, pharmaceutical and environmental applications.