Filtration vs Ethanol Precipitation

Introduction

When selecting the water capture method for the water vole environmental DNA (eDNA) analysis service, two main considerations were identified;

While it is essential that the probability of detecting the presence of water vole eDNA is as high as possible, ecologists must be able to take samples and transport the samples to the lab without unnecessary time, labour and financial costs. This document briefly describes the reasoning behind on-site filtration being selected as the water sampling method for water vole eDNA.

Maximising water vole detection:

There is a solid base of published scientific papers that have studied the effect of different methods of water sampling on eDNA analysis accuracy and reliability. The best known application of eDNA analysis in the UK, the method used to detect the great crested newt, utilises a method known as ethanol precipitation to capture eDNA (Thomsen et al. 2012). However, this has been shown to not be the optimum eDNA capture method. Deiner et al. (2015) carried out a comprehensive comparison of different eDNA capture and extraction combinations. This study identified that filtration of the water sample using specialist filter papers was the optimum method for the detection of macroorganism eDNA.

Suitability as a survey method:

As such, ecologists must be able to transport the sampling kit to site, collect the water sample and return the samples to the lab quickly and safely. Filtration using a syringe and filter cartridge is a simple method that allows the water sample to be filtered on-site. Ethanol is then added to the filtration unit to preserve the DNA. This method can be completed within 20-40 minutes, limits transport costs and prevents degradation of DNA while in transit.

Conclusion:

Our current methods reflect the best practices, based upon the evidence currently available. As our knowledge of the technique increases with experience and new evidence comes to light, the method may be amended. Updated protocols will be uploaded to our website and sent with each sampling kit.

If you have any questions regarding our on-site water filtration method or you have any feedback / ideas for improving the current method, get in contact at lab@crestwoodenvironmental.co.uk or call 01902 229 563.