Abstract
ObjectiveSilica gel beads have promise as a non-toxic, cost-effective, portable method for storing environmental DNA (eDNA) immobilized on filter membranes. Consequently, many ecological surveys are turning to silica bead filter desiccation rather than ethanol preservation. However, no systematic evaluation of silica bead storage conditions or duration past 1 week has been published. The present study evaluates the quality of filter-immobilized eDNA desiccated with silica gel under different storage conditions for over a year using targeted quantitative real-time polymerase chain reaction (qPCR)-based assays.ResultsWhile the detection of relatively abundant eDNA target was stable over 15 months from either ethanol- or silica gel-preserved filters at − 20 and 4 °C, silica gel out-performed ethanol preservation at 23 °C by preventing a progressive decrease in eDNA sample quality. Silica gel filter desiccation preserved low abundance eDNA equally well up to 1 month regardless of storage temperature (18, 4, or − 20 °C). However only storage at − 20 °C prevented a noticeable decrease in detectability at 5 and 12 months. The results indicate that brief storage of eDNA filters with silica gel beads up to 1 month can be successfully accomplished at a range of temperatures. However, longer-term storage should be at − 20 °C to maximize sample integrity.
Highlights
Over the past decade, techniques used to detect environmental DNA—genetic material present in environmental samples from secretions, excretions, exogenous sloughing of eukaryotic cells, or from microscopic organisms [1]—have surged in use by academic, government, conservation, and development sectors for providing cost-effective information about at-risk and invasive species in natural and managed ecosystems [2–5]
The results indicate that brief storage of environmental DNA (eDNA) filters with silica gel beads up to 1 month can be successfully accomplished at a range of temperatures
Filters that were stored in ethanol at 23 °C experienced a progressive decrease in eDNA sample quality across all time points compared to filter samples that were processed immediately
Summary
While the detection of relatively abundant eDNA target was stable over 15 months from either ethanol- or silica gel-preserved filters at − 20 and 4 °C, silica gel out-performed ethanol preservation at 23 °C by preventing a progressive decrease in eDNA sample quality. Silica gel filter desiccation preserved low abundance eDNA well up to 1 month regardless of storage temperature (18, 4, or − 20 °C). Only storage at − 20 °C prevented a noticeable decrease in detectability at 5 and 12 months. The results indicate that brief storage of eDNA filters with silica gel beads up to 1 month can be successfully accomplished at a range of temperatures. Longer-term storage should be at − 20 °C to maximize sample integrity
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