Determination of dissolved nucleic acids in seawater by the fluorescence dye, ethidium bromide

Abstract

A new method for the determination of dissolved double-stranded deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in seawater was developed, evaluated and used to study the fates of these nucleic acids in marine ecosystems. These nucleic acids, which were pre-concentrated on a hydroxyapatite column, were determined fluorometrically by the use of ethidium bromide dye, which binds specifically to the double-stranded polynucleotide. No dissolved organic matter coexisting in the pre-concentrated sample solution interfered in the analysis of DNA and RNA. Column recoveries of DNA and RNA in a sample volume of up to 11 were 93% and 97%, respectively, and 90% of both at 51. The detection limits of DNA and RNA concentrated from a 51 sample by this fluorometric method were 0.6 and 1.1 μg l −1, respectively. The concentration of dissolved nucleic acids in the waters from Tokyo Bay and Sagami Bay showed great variation in space and time. DNA ranged from 1 to 32 μg l −1, and RNA from below the detection limit to 34 μg l −1. The total amount of phosphorus in nucleic acids was an important fraction (12.9 ± 8.2%) of the dissolved organic phosphorus (DOP) and showed a good correlation with DOP.