Direct extraction of microbial community DNA from humified upland soils

This paper describes a protocol effective at extracting high yields of high-purity microbial community DNA from humified soils. DNA was extracted from soil by lysozyme, SDS and freeze–thaw lysis, precipitated and then subjected to a double caesium chloride density gradient centrifugation stage before concentrating and washing. Evaluation using three soils yielded up to 30 μg DNA g−1 dry soil, with absorbance ratios at 260 : 230 nm and 260 : 280 nm of 1·6–2·0. The DNA extracted from the three soils was digested by four restriction enzymes and a 16S rDNA eubacterial product was amplified by PCR. These tests indicated that the DNA obtained by the protocol was sufficiently pure for molecular biological analysis.