Consideration of eDNA states to analyze bulk soil samples via metabarcoding

Environmental DNA (eDNA) analysis can facilitate biodiversity monitoring within a bulk sample, especially valuable to evaluate soil ecosystems. eDNA can persist in soil as living cells, dead cells, and extracellular DNA either as free or adsorbed to particles in the soil. Each of these ‘states’ of eDNA can have differing persistence times from a few days to hundreds of years. Better understanding to target and isolate particular states of eDNA is imperative to derive valuable information, for instance, recent occupancy indicated by freshly released eDNA or eDNA within living cells.

This presentation will present cases showing the variability of eDNA persistence in different states with a focus on the adsorbed state. I will then discuss the adsorption mechanism of eDNA and introduce novel methods of isolating the states of eDNA from a single sample for independent analysis. Lastly, I will show data from a landscape level study with water samples collected from 221 sites from 58 streams in eight Swiss watersheds. All the samples were state sorted and analyzed with board range metabarcoding assays for identifying metazoan diversity. The results show that each state consists of unique diversity information and state sorting methodologies should be considered when processing bulk soil samples for eDNA analysis. While this presentation will have some studies using water samples, they elucidate the behavior of eDNA bound to soil and sediment particles as well.