Research Product

The mechanisms of utilization of DNA by estuarine microbial populations has been investigated by competition experiments and DNA uptake studies. Deoxyribonucleoside monophosphates (dNMP's), thymidine, thymine, and RNA all competed with the uptake of radioactivity from [3H]DNA in 4 hour incubations. In fifteen minute incubations, dNMP's had no effect or stimulated [3H]DNA binding, depending on concentration. Uptake of radioactivity from [3H]DNA resulted in little accumulation of TCA-soluble intracellular radioactivity, and was inhibited by the DNA synthesis inhibitor novobiocin. Molecular fractionation studies indicated that some [3H]DNA appeared in the RNA (10 and 30% at 4 and 24 h respectively) and protein (approximately 3%) fractions. The ability for estuarine microbial assemblages to transport gene sequences was investigated by plasmid uptake studies followed by molecular probing. Although plasmid DNA was detected on filters after filtration of plasmid-amended incubations, DNase treatment of filters removed this DNA, indicating little transport of intact gene sequences. These observations lead to the following model for DNA utilization by estuarine microbial populations: 1) DNA is rapidly bound to the cell surface and 2) hydrolyzed by cell-associated and extracellular non-specific nucleases. 3) DNA hydrolysis products are transported and 4) rapidly salvaged into nucleic acids with little accumulation into intracellular nucleotide pools.