On-site filtration of water samples for environmental DNA analysis to avoid DNA degradation during transportation

Environmental DNA (eDNA) analysis is an innovative tool for determining the distribution or abundance of aquatic macroorganisms. However, because eDNA degrades rapidly in water, long delays between sampling and analysis may hinder eDNA quantification. In the present study, we developed a portable filtration system that enables on-site (and on-the-road) filtration of water samples. Degradation rates of eDNA within 6 h were compared using water from an outdoor pond that was subjected to (1) on-site filtration, (2) transportation of water on ice, and (3) transportation of water at ambient temperature. Groups 2 and 3 were filtered in the laboratory 6 h after sampling. The concentration of eDNA was determined as the copy number of the mitochondrial cytochrome b gene of two fish species using real-time polymerase chain reaction. The portable filtration system offers the following benefits: (1) the eDNA concentration is preserved as is at the time of sampling, permitting higher accuracy of eDNA quantification, (2) use of a disposable sealed plastic bag reduces the risk of contamination and ensures on-the-road filtration, (3) time is saved because filtration can be accomplished when driving between sampling sites.