Combined lipid/DNA extraction method for environmental samples

Abstract Previously, separate methods have been developed for the extraction and purification of lipids and DNA from soils and sediments. This paper describes a new method for the isolation of both lipids and DNA from the same environmental sample. This combined method is based on the Bligh and Dyer lipid extraction technique. Upon phase separation, lipids partition into the organic phase and DNA partitions into the aqueous phase. DNA extraction and recovery from the solid phase is necessary under certain conditions. Preliminary experiments performed with 32 P-labeled DNA in the absence of soil showed that greater than 98% of the total DNA was present in the aqueous phase after the modified Bligh and Dyer extraction. Analysis of the DNA by polyacrylamide gel electrophoresis and autoradiography demonstrated that no degradation of DNA occurred during the lipid extraction procedure. Lipid extraction of lyophilized cells showed that DNA was released from Pseudomonas putida and Bacillus subtilis cells corresponding to 26±5 and 14±4% of the theoretical DNA yield, respectively. The combined lipid/DNA extraction method was applied to both lyophilized cells and wet cells added to soil. Analysis by DNA:DNA hybridization showed that approx. 40–50% of the DNA from cells added to soil was recovered after lipid extraction relative to samples treated only with conventional DNA extraction. Estimation of cell number per gram soil based on either lipid or DNA analysis showed good agreement with actual numbers added based on plate counts of the inocula. DNA extracts from samples which had been lipid-extracted also had lower amounts of humic material. Although some DNA was not recovered after lipid extraction, that which was recovered was of sufficiently high quality for hybridization analysis. This method shows utility for the co-recovery of both lipids and DNA from a single sample; this is particularly useful when a small sample size is all that is available or procurable.