Validation and application of diphenylamine method for DNA detection into soils and clay minerals

Purpose

Soil provides important ecosystemic services, in particular through its biodiversity, which plays a major role for humans. It is therefore essential to detect and, above all, quantify soil DNA in order to better understand and conserve this biodiversity. However, the techniques commonly used are not specific and do not always allow an easy and reliable detection in complex matrices rich in organic matter. The aim of this article is to develop an effective method to quantify DNA whatever the type of soil matrix.

Materials and methods

Two reference clays (kaolinite and montmorillonite which are ubiquitous in soils but present very different physicochemical properties) and two soils (Cambisols and Andosols with different mineralogy, organic matter content, and properties) were used for this purpose. The developed method, based on the use of diphenylamine with colorimetric detection at 600 nm, was compared to the traditional method (absorption at 260 nm).

Results and discussion

The results highlight the independence of the method in terms of organic matter content or soil type, as well as its simplicity and low cost. It opens up important possibilities of application, such as a better understanding of the interactions between DNA and mineral supports, as well as the effects of mineral species. As an illustration, the method was applied to study the sorption of calf thymus DNA on various substrates with or without humic acid for a specific concentration. DNA sorption has been successfully adjusted by the Langmuir model.

Conclusions

The method is specific and can be easily used in complex matrices commonly found in soils, regardless of the different properties in terms of mineralogical content, presence of organic matter, or physicochemical properties.