Mechanism of eDNA Adherence to Materials
The mechanism by which eDNA adheres to materials in natural aquatic systems remains unclear.
We used scanning electron microscopy to gain insight into the mechanism of attachment but found no consistent patterns. Despite trialling materials with a range of surface complexities, we found no supporting evidence that eDNA was entrapped within the interstitial spaces of the materials. Rather, biological matter appeared to adhere randomly to any available surface and showed great diversity in size and shape. For example, morphologically distinct single cell eukaryotes and bacteria could be seen on the surfaces of the membrane materials, many embedded in larger bodies of seemly biological material, most likely biofilm. An important component of biofilm development is extracellular polymeric substances (Hancock 2001, Vilain et al. 2009) which are mainly comprised of polysaccharides, proteins, metabolites and extracellular DNA (Das et al. 2013). These extracellular polymeric substances occur in a range of molecular sizes, conformations and physical/chemical properties and although little is known about the physical ultrastructure of how they interact (Decho and Gutierrez 2017), they are known to adhere to both natural and engineered surfaces (Das et al. 2013). The diversity of biological compounds and structures that eDNA might be associated with in aquatic systems is huge. Dissolved organic matter (DOM) may contain more than 20,000 compounds in a single seawater sample (Mentges et al. 2017). Particulate organic matter (POM) as seen in Figure 6 contains equal or greater diversity as well as structural complexity because much of it is derived from dead organisms (Kharbush et al. 2020). A deeper understanding of the adhesive properties of different fractions of the POM pool and biofilms associated with passive eDNA collection materials may provide deeper insights into eDNA binding to collection materials.