Biofilm on microplastics - a biophysical perspective

Microplastics (MPs) are small pieces of plastic between 1 μm and 5 mm in size, that occur in the environment as a consequence of plastic pollution, and their ubiquitous presence in water has become a major threat to ecosystems. Once MPs enter marine and freshwater environments, they come into contact with organic matter, nutrients, and microorganisms, such as bacteria, algae and fungi. Very soon after, these microorganisms aggregate on the surface of the plastic particles and form colonies that gradually create a complex biological layer, called a biofilm. This biofouling process may affect the ecological risks of MPs and contribute to increased antimicrobial resistance. It can also alter the physical and chemical properties of MPs, which may, in turn, affect how these particles move in the water, such as whether they will float or sink (sinking behaviour) and how far from their release source they can travel (environmental transport). Our understanding of the influence of biofilms on the transport of MPs in aquatic environments remains limited, warranting further research on microbe-MP interactions. BIOPHYLM aims to investigate the physicochemical changes occurring to MPs during biofilm formation, focusing on particle size, density and surface morphology to increase our knowledge of how biofilms affect the particles’ mobility and thus assist in better-informed models of MP transport in the environment. For this purpose, MP particles will be exposed to river water (Donau kanal, Vienna) and biophysical, colloidal, and high-throughput sequencing approaches will be applied for studying microbe-plastic interactions, measuring biofilm growth, and assessing particle mobility and sinking behaviour. Notably, the project will focus on a less-investigated, yet significant aspect, which is the lower end of the MP size range, between 1-100 μm. In addition, BIOPHYLM will attempt real-time measurements of biofilm growth and MP particle mobility by using in-line digital holographic microscopy, a pioneering technology recently developed by BOKU researchers. By linking data from each technique, BIOPHYLM aspires to obtain a holistic view of MP-microbe interactions and fill important knowledge gaps that will improve our understanding of the role of biofilm on MP transport, and thus reinforce a science-based risk assessment of plastic particles in the aquatic environment.