THYMIDINE INCORPORATION INTO SOIL BACTERIA

Bacterial growth rates in a sandy loam soil and a forest humus were estimated using [3H]thymidine incorporation into DNA. Soil DNA was separated from other macromolecules using an acid-base hydrolysis method, since label was incorporated into protein. Using this method, recovery of added [14C]DNA was 58% from the humus and 75% from the sandy loam. Specificity of [3H]thymidine incorporation into bacterial DNA was indicated by studying the effects of different fungal and bacterial inhibitors. Further, a consortium of 15 soil fungi did not incorporate thymidine during short-term incubations. The rate of thymidine incorporation was constant for at least 60 min after the addition of thymidine (2.2 μm) to the sandy loam. The specific thymidine incorporation rate at 23°C was 10.5 × 10-21 mol bacterial cell-1 h-1 in the sandy loam and 8.8 × 10-21 mol cell-1 h-1 in the humus. Using conversion factors from the literature an annual turnover of bacterial cells of 14 to 28 times was calculated in the humus. © 1990.