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 been devoted to the elaboration of an effective purification method but none appears universal. During our investigations of soil bacterial changes induced by soil-feeding termites, we found that humic acid content usually impede DNA purification. Indeed, humic acids and nucleic acids share similar physicochemical properties. Here, we tested eight purification procedures including electrophoretical and chromatographical methods. The results show for DNA extracted from humic rich samples, e.g. termite mounds, that only the combination of two methods gave a DNA sufficiently pure to perform successful amplifications.