EFFECTS OF RADIOACTIVE LABELING OF MACROMOLECULES, DISTURBANCE OF BACTERIA AND ADSORPTION OF THYMIDINE TO SEDIMENT ON THE DETERMINATION OF BACTERIAL-GROWTH RATES IN SEDIMENT WITH TRITIATED-THYMIDINE

The rates of [methyl-3H]thymidine incorporation into DNA were used to determine bacterial growth rates in seagrass sediments. The distribution of radioactivity in macromolecules extracted from the sediment was determined by hydrolytic enzymes that were specific for DNase and protein. In the extracts that were presumed to contain DNA, and in which radioactivity was determined, it was confirmed that at least 85% of the radioactivity was in DNA after a 15-min incubation with tritiated thymidine and only 6% was in protein; the remainder was not characterised. Macromolecules, other than DNA, in the extracts were substantially labelled only after prolonged incubation. Bacterial DNA synthesis did not appear to be affected immediately by small changes in the sediment's microenvironment. A simple experiment is described for determining the amount of sediment to use in the thymidine incubation so as to minimize problems with isotope dilution due to adsorption of thymidine to the sediment. © 1990.