Particle size distribution and optimal capture of aqueous macrobial eDNA

1. Detecting aquatic macroorganisms with environmental DNA (eDNA) is a new survey method with broad applicability. However, the origin, state, and fate of aqueous macrobial eDNA - which collectively determine how well eDNA can serve as a proxy for directly observing organisms and how eDNA should be captured, purified, and assayed - are poorly understood. 2. The size of aquatic particles provides clues about their origin, state, and fate. We used sequential filtration size fractionation to measure, for the first time, the particle size distribution (PSD) of macrobial eDNA, specifically Common Carp (hereafter referred to as Carp) eDNA. We compared it to the PSDs of total eDNA (from all organisms) and suspended particle matter (SPM). We quantified Carp mitochondrial eDNA using a custom qPCR assay, total eDNA with fluorometry, and SPM with gravimetric analysis. 3. In a lake and a pond, we found Carp eDNA in particles from >180 to <0.2 μm, but it was most abundant from 1-10 μm. Total eDNA was most abundant below 0.2 μm and SPM was most abundant above 100 μm. SPM was ≤0.1% total eDNA, and total eDNA was ≤0.0004% Carp eDNA. 0.2 μm filtration maximized Carp eDNA capture (85%±6%) while minimizing total (i.e., non-target) eDNA captu...Continue Reading