THYMIDINE INCORPORATION INTO MACROMOLECULES OF BACTERIA EXTRACTED FROM SOIL BY HOMOGENIZATION CENTRIFUGATION

The growth rate of bacteria extracted from two different soil types by homogenization-centrifugation was estimated with the [H-3]thymidine incorporation technique. No change in thymidine incorporation rate was found up to 4 h after the preparation of the bacterial solution using distilled water. Radioactivity was also incorporated into RNA and protein. This nonspecific labelling started immediately and appeared linear over time. Incorporation of radioactivity into DNA was about 40%, into RNA 40% and into protein 20%, of incorporation into total macromolecules. The thymidine incorporation rate decreased after addition of Ringer solution, 0.9% NaCl, Winogradsky's salt solution, 50 mM K2HPO4, 50 mM CaCl2, 0.2% Calgon or 0.2% sodium pyrophosphate compared to distilled water alone. Lower concentrations of these additives had lower or negligible effects. The specific incorporation rate at 22-degrees-C for bacteria extracted by homogenization-centrifugation was 6.0 x 10(-21) mol thymidine cell-1 h-1 for a sandy loam and 4.4 x 10(-21) mol thymidine cell-1 h-1 for an acid organic soil. This corresponds to a turnover time of 3.5 days for bacteria from the sandy loam and 4.8 days for bacteria from the organic soil using a conversion factor of 2 x 10(18) cells mol-1 thymidine.