Purification and isotopic signatures (δ13C, δ 15N, Δ14C) of soil extracellular DNA

The aim of this work was to obtain pure extracellular DNA molecules so as to estimate their longevity in soil by an isotope-based approach. Extracellular DNA molecules were extracted from all horizons of a forest soil and purified by the procedure of Davis ( Purification and precipitation of genomic DNA with phenol-chloroform and ethanol. In: Davis LG, Dibner MD, Battey JF ( eds) Basic methods in molecular biology. Appleton & Lange, Norwalk, 16 - 22, 1986) without ( DNA1) or with ( DNA2) a successive treatment with binding resins followed by elution. The two differently purified DNA samples were compared for their A(260)/A(280) ratio, polymerase chain reaction ( PCR) amplification and natural abundance of stable ( C-13 and N-15) and radioactive ( C-14) isotopes. The purity index and the PCR amplification did not differentiate the efficiency of the two purification procedures. The isotopic signature of DNA was more sensitive and was strongly affected by the purification procedures. The isotopic measurements showed that the major contaminant of extracellular DNA1 was the soil organic matter ( SOM), even if it is not possible to exclude that the similar delta C-13, delta N-15 and Delta C-14 values of DNA and SOM could be due to the use of SOM-deriving C and N atoms for the microbial synthesis of DNA. For extracellular