Genetic material in the marine environment: Implication for bacterial DNA

Particulate DNA content (DNA p ) in water samples from freshwater, estuarine, and marine environments was measured with the DNA‐specific fluorochrome Hoechst 33258. A good correlation ( r = 0.94) was found between DNA content and bacterial number for all samples. Size fractionation with 12‐, 3‐, and 1‐ µ m Nuclepore filters indicated that the 0.2‐–‐ µ m fraction contained 40–54% of the total DNA p of fresh/brackish and 71–91% of that of oceanic waters. This fraction also contained most of the bacterioplankton, while the phytoplankton (as indicated by Chl a ) was found primarily in the 12–110‐ µ m fraction. The results suggest that most of the DNA p in the marine environment is associated with bacterioplankton and not with phytoplankton.