Identification and analysis of nucleic acids in natural freshwaters

Abstract

A method was developed for the identification and subsequent purification of extracellular nucleic acids from natural freshwater samples of 250–1000 ml. Most sites contained DNA in two distinct size classes but no detectable RNA. The large DNA size class, > 20 kb, was mainly viral in origin (vDNA) whereas the smaller DNA of 100–500 bp (sDNA) was from unknown sources. Both types were concentrated effectively with high yield by DEAE-Sephacel chromatography and were separable from each other by preparative electrophoresis. Purification to homogeneity required a further chromatography step using hydroxyapatite. Electron microscopy suggested that vDNA was probably mainly of bacteriophage origin.