Abundance of Virus-Sized Non-DNase-Digestible DNA (Coated DNA) in Eutrophic Seawater

Total DNA concentration in 0.2-mum-pore-size Nuclepore filter filtrates (<0.2-mum fraction) of Tokyo Bay water was estimated to be 9 to 19 ng/ml by an immunochemical quantification method. Almost 90% of the DNA in the <0.2-mum fraction was found in the size fractions larger than 3.0 x 10 Da and 0.03 mum, and most was not susceptible to DNase digestion, that is, consisted of non-DNase-digestible DNA (coated DNA). A significant amount of DNA was obtained from the <0.2-mum fraction of the seawater by three different methods: polyethylene glycol precipitation, direct ethanol precipitation, and ultrafilter concentration. Gel electrophoresis analysis of the isolated DNAs showed that they consisted mainly of coated DNAs with a similar molecular sizes (20 to 30 kb [1.3 x 10 to 2.0 x 10 Da). The abundance of the ultramicron virus-sized coated DNA in natural seawater suggests that these DNA-rich particles can be attributed to marine DNA virus assemblages and that they may be a significant phosphorus reservoir in the environment.