Distribution and molecular weight of dissolved DNA in subtropical estuarine and oceanic environments

Abstract

Dissolved DNA and a series of microbial biomass and activity parameters were measured in offshore, coastal, estuanne and coral reef environments of the southeast Gulf of Mexico. Oceanic concentrations of dissolved DNA ranged from 0.2 to 19 vg 1-' and decreased as a function of distance from shore and depth in the water column. Dissolved DNA concentrations were greater than half the particulate DNA content in offshore environments (Z = 63 + 45 O/O), but were a smaller percentage of particulate DNA in nearshore and estuarine environments (Z = 35 f 21 %). Dissolved DNA correlated better with bacterial parameters (i.e. bacterial direct counts, particulate DNA and thymidine incorpora-tion) than with phytoplankton parameters (chlorophyll a, primary productivity). The molecular weight (MW) of dissolved DNA (determined by agarose gel electrophoresis) ranged from 0.12 kilobase pairs (kb; 7.75 X 104 daltons) to 35.2 kb (2.32 X 10' daltons) for estuarine samples, while an oligotrophic environment contained smaller MW DNA (range 0.24 to 14.27 kb). DNA fragments in this size range are sufficient to contain gene sequences. These results are discussed in terms of the potential for transfor-mation by dissolved DNA.