1. Aqueous environmental DNA (eDNA) is an emerging efficient non-invasive tool for species inventory studies.
To maximize performance of downstream quantitative PCR (qPCR) and next-generation sequencing (NGS)
applications, quality and quantity of the starting material is crucial, calling for optimized capture, storage and
extraction techniques of eDNA. Previous comparative studies for eDNA capture/storage have tested precipitation and ‘open’ filters. However, practical ‘enclosed’ filters which reduce unnecessary handling have not been
included. Here, we fill this gap by comparing a filter capsule (Sterivex-GP polyethersulfone, pore size 022 lm,
hereafter called SX) with commonly used methods.
2. Our experimental set-up, covering altogether 41 treatments combining capture by precipitation or filtration
with different preservation techniques and storage times, sampled one single lake (and a fish-free control pond).
We selected documented capture methods that have successfully targeted a wide range of fauna. The eDNA was
extracted using an optimized protocol modified from the DNeasy Blood & Tissue kit (Qiagen). We measured
total eDNA concentrations and Cq-values (cycles used for DNA quantification by qPCR) to target specific
mtDNA cytochrome b (cyt b) sequences in two local keystone fish species.
3. SX yielded higher amounts of total eDNA along with lower Cq-values than polycarbonate track-etched filters
(PCTE), glass fibre filters (GF) or ethanol precipitation (EP). SX also generated lower Cq-values than cellulose
nitrate filters (CN) for one of the target species. DNA integrity of SX samples did not decrease significantly after
2 weeks of storage in contrast to GF and PCTE. Adding preservative before storage improved SX results.
4. In conclusion, we recommend SX filters (originally designed for filtering micro-organisms) as an efficient capture method for sampling macrobial eDNA. Ethanol or Longmire’s buffer preservation of SX immediately after
filtration is recommended. Preserved SX capsules may be stored at room temperature for at least 2 weeks without significant degradation. Reduced handling and less exposure to outside stress compared with other filters
may contribute to better eDNA results. SX capsules are easily transported and enable eDNA sampling in remote
and harsh field conditions as samples can be filtered/preserved on site.