IDENTIFICATION AND ANALYSIS OF NUCLEIC-ACIDS IN NATURAL FRESH-WATERS

A method was developed for the identification and subsequent purificat ion 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 vira l in origin (vDNA) whereas the smaller DNA of 100-500 bp (sDNA) was fr om unknown sources. Both types were concentrated effectively with high yield by DEAE-Sephacel chromatography and were separable from each ot her by preparative electrophoresis. Purification to homogeneity requir ed a further chromatography step using hydroxyapatite. Electron micros copy suggested that vDNA was probably mainly of bacteriophage origin.