Exposure to Silver Nanoparticles Affects Biofilm Structure and Adhesiveness

The effect of citrate-coated silver nanoparticle (AgNPs) exposure on biofilm structure and adhesiveness was investigated by a multiphasic approach comprising epifluorescence microscopy, chemical analysis and enhanced magnetic particle induction (MagPI). Mono-species biofilms of the ubiquitous freshwater bacterium Aquabacterium citratiphilum were treated with two different concentrations of AgNPs. Control experiments were performed with untreated Aquabacterium biofilms and with biofilms exposed to ionic silver (AgNO3) and copper sulphate (CuSO4). The biofilm structure was assessed using epifluorescence microscopy and the composition of colloidal extracellular polymeric substances (EPS) was determined spectrophotometrically after extraction. The biofilm adhesiveness was measured using an enhanced MagPI system. The overall contents of EPS proteins and carbohydrates as well as the mean surface coverage by biofilm bacteria were significantly reduced in all treatments. The exposure to 600 μg l-1 AgNPs significantly reduced the biofilm adhesiveness (p<0.0001, n=50) to a level equivalent to biofilms treated with AgNO3 and CuSO4. The results demonstrate the impact of an exposure to environmentally relevant concentrations of engineered AgNPs on the Aquabacterium biofilm composition and structure and biofilm adhesiveness as a physical trait. Enhanced MagPI could be successfully proven to be a rapid and sensitive technique for the assessment of biofilm adhesiveness as an essential marker for biofilm functionality and correlated biofilm ecosystem services (e.g. microbial biostabilization).