Natural abundance δ15N and δ13C of DNA extracted from soil

We report the first simultaneous measurements of delta N-15 and delta C-13 of DNA extracted from surface soils. The isotopic composition of DNA differed significantly among nine different soils. The delta C-13 and delta N-15 of DNA was correlated with delta C-13 and delta N-15 of soil, respectively, suggesting that the isotopic composition of DNA is strongly influenced by the isotopic composition of soil organic matter. However, in all samples DNA was enriched in C-13 relative to soil, indicating microorganisms fractionated C during assimilation or preferentially used C-13 enriched substrates. Enrichment of DNA in N-15 relative to soil was not consistently observed, but there were significant differences between delta N-15 of DNA and delta N-15 of soil for three different sites, suggesting microorganisms are fractionating N or preferentially using N substrates at different rates across these contrasting ecosystems. There was a strong linear correlation between delta N-15 of DNA and delta N-15 of the microbial biomass, which indicated DNA was depleted in N-15 relative to the microbial biomass by approximately 3.4%(o). Our results show that accurate and precise isotopic measurements of C and N in DNA extracted from the soil are feasible, and that these analyses may provide powerful tools for elucidating C and N cycling processes through soil microorganisms. (C) 2007 Elsevier Ltd. All rights reserved.