Evaluation of purification procedures for DNA extracted from organic rich samples: Interference with humic substances

A limitation of the use of the Polymerase Chain Reaction (PCR) for soil DNA analysis is the contamination by humic substances. Numerous studies have b een devoted to the elaboration of an effective purification method but none appears universal. During our investigations of soil bacterial changes ind uced by soil-feeding termites, we found that humic acid content usually imp ede DNA purification. Indeed, humic acids and nucleic acids share similar p hysicochemical properties. Here, we tested eight purification procedures in cluding electrophoretical and chromatographical methods. The results show f or DNA extracted from humic rich samples, e.g. termite mounds, that only th e combination of two methods gave a DNA sufficiently pure to perform succes sful amplifications.