Excretory overexpression of hydrophobins as multifunctional biosurfactants in E. coli

Hydrophobins are small amphipathic proteins excreted from filamentous fungi that self-assemble into the amphipathic film at hydrophobic/hydrophilic interfaces and can be used in a wide range of biotechnological application such as antimicrobial coatings, biosensors, and drug delivery. Here we describe a simple method for producing functionally active class I and class II hydrophobins in E. coli. The class I hydrophobin EAS (rodlet protein) from Neurospora crassa and class II hydrophobin HFBII from Trichoderma reesei were separately fused with fusion partner Ffu312 (β-fructofuranosidase truncation with a native signal peptide) and successfully expressed in E. coli. Significantly, fused hydrophobins Ffu312-EAS and Ffu312-HFBII were excreted into the culture medium. The excretory expression of hydrophobins facilitated the correct disulfide-bond formation and simplified the purification. Both fusion hydrophobins reversed the glass surface hydrophilicity, reduced the water surface tension and improved emulsion stability. Ffu312 has little effect on surface coating, water surface tension and emulsion stabilization of hydrophobins. This study may provide an efficient approach for excretory and functional expression of class I and class II hydrophobins in E. coli.