Streptomyces bacteria are highly versatile micro-organisms, which have been recognised as potent soil, (bio)chemical and (bio)material engineers. Streptomyces has served as a source of inspiration for materials development in vitro, based on their ability to modulate in vivo the properties of its own surface and that of its natural environment. Our interdisciplinary projects have developed Chaplins, functional amyloid proteins from Streptomyces bacteria, into novel nano-thin anti-corrosion coatings and as adhesive materials for the manufacturing and defence industry.
Chaplin proteins were extracted from a range of wild-type strains, while a synthetic promoter system was developed to express and secrete chaplins, which are typically difficult to express and purify. Chaplin proteins were found to have useful anticorrosive properties as protein-only coatings. Unmodified chaplin protein was coated onto different steel and magnesium substrates, through one or more applications, thereby creating barrier layers of tens to hundreds of nm thickness. A chemical corrosion inhibitor could also be covalently bound to chaplin protein, which retained the ability to coat substrates. Corrosion resistance improved upon multiple coatings with chaplin protein as determined by exposure to salt solutions using Electrochemical Impedance Spectroscopy and low-and higher resolution materials characterization techniques such as goniometry, hydrogen evolution, Scanning Vibrating Electrode Technique (SVET) and the Kelvin Scanning Probe (KSP). Chaplins also have a role in the strong adhesion of Streptomyces to solid substrates in vivo. The bonding abilities of natural and engineered chaplins were determined in vitro by bonding glass and polycarbonate coupons to yield glass laminates. Chaplins have thus been developed into a fast-curing optically transparent adhesive material when combined with a partner biocomposite material. Current efforts focus on upscaling of production and downstream processing. Thus, our anti-corrosive protein coating and protein-based adhesive applications have great potential for the manufacturing, defence and other industries, including healthcare and biomaterials manufacturing.