Recombinant hydrophobin coated surfaces and their influence on microbial biofilm formation

Annika Rieder^1*, Tatjana Ladnorg², Christof Wöll², Ursula Obst¹, Reinhard Fischer³, Thomas Schwartz¹

¹ Karlsruhe Institute of Technology, Institute of Functional Interfaces, Department of Interface Microbiology, P.O. Box 3640, 76021 Karlsruhe, Germany

² Karlsruhe Institute of Technology, Institute of Functional Interfaces, Department of Surface Chemistry, P.O. Box 3640, 76021 Karlsruhe, Germany

³ Karlsruhe Institute of Technology, Institute for Applied Biosciences, Department of Microbiology, Hertzstr. 16, 76187 Karlsruhe, Germany

* presenting author

Biofilms represent a very successful symbiotic life form of microorganisms. They play an ambivalent role in industrial systems and can not be avoided on a great variety of surfaces. However, the characteristics of a material and its corresponding surface properties affect the biocompatibility and consequently bacterial adhesion and biofilm growth.

In this approach recombinant fusion hydrophobins were used for surface modification. Hydrophobins are non-toxic and non-immunogenic fungal proteins which self-assemble on different surfaces into extremely stable monolayers in an amphiphilic manner. Recombinant hydrophobins provide the opportunity to use these surface-active proteins for large-scale surface modification of industrial and medical relevant materials.

Thus, protocols for surface coating with recombinant fusion hydrophobins were developed. Quartz crystal microbalance measurements were used to analyze the adsorption behaviour of the fusion hydrophobins. The hydrophobin coatings were characterized with water contact angle measurements, immunofluorescence microscopy and atomic force microscopy in terms of hydrophobicity and homogeneity. The self-assembly process of the recombinant fusion hydrophobins depended on the incubation temperature and the incubation time. Fusion hydrophobins are as well suited as natural hydrophobins for surface modification.

To test the possible application of hydrophobins for antifouling coatings, the growth behaviour of various microorganisms was studied on hydrophobin modified versus unmodified glass surfaces. Single bacterial strains as well as natural bacterial communities were used to analyse biofilm formation. Apart from conventional plating experiments, fluorescence microscopy and molecular-biological methods such as denaturing gradient gel electrophoresis were applied to determine differences in the biofilm growth. The results demonstrated that the change of surface hydrophobicity and the fusion hydrophobins itself did not affect the biofilm formation.

Due to their self-assembly properties, fusion hydrophobins can be used for effective large-scale surface coating in monolayer manner. To stimulate the effect on biofilm formation the hydrophobins can subsequently be functionalized with already bioactive molecules like antimicrobial peptides to influence the bacterial adhesion.