The influence of copper and silver ions on Cupriavidus metallidurans biofilm formation and development

Bacterial biofilm formation is a widely known problem for water storage and distribution systems since it often leads to recurring contamination and water spoilage. Cupriavidus metallidurans strains, such as NA4, have been discovered aboard the International Space Station (ISS). Their presence is notable, especially in water supplies, because of the absence of nutrients and the presence of water decontaminants such as silver. C. metallidurans, and in particular strain CH34, is mostly studied for its metal resistance. Both C. metallidurans CH34 and NA4 are able to form biofilms. The aim of this thesis was to study C. metallidurans biofilms in the presence of various concentrations of copper (Cu2+) and silver (Ag+), since these metal ions are frequently used as water disinfectants.
Biofilm formation and development were studied in Lysogeny broth (LB) medium and Tris-buffered mineral (284) medium. Optical density (OD) measurements, crystal violet (CV) quantification, RNA extraction, and scanning electron microscopy (SEM) were carried out in order to determine the effect of silver and copper ions on biofilm formation. In 284 medium, an inhibiting effect on biofilm growth was found for 5 μM Ag+ and 5 mM Cu2+. RNA extraction of biofilms was performed, but optimization of the extraction protocol is needed. Furthermore, SEM visualised interesting structural differences in CH34 and NA4 biofilm formation, revealing a more developed extracellular polymeric substance (EPS) structure of CH34 biofilm and a higher density of NA4 biofilms.