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.