DETERMINATION OF BACTERIAL DNA IN SOIL

Two methods for the determination of DNA have been adapted for use on the bacterial fraction of an organic soil, obtained by fractionated centrifugation. The. soil contained about 1.1 × 1010 bacteria g-1 dry weight when counted by fluorescence microscopy. One method was based on the reaction with 3,5-diaminobenzoic acid 2HCl, and the other on the specific reaction of the antibiotic mithramycin with double-stranded DNA. For the first method, about 8 × 108 cells were required and for the second, about 4 × 109. The analytical results with the two methods agreed well. As an average of several determinations, an amount of 8.4 fg (10-15g) DNA per bacterial cell was found when the cells were counted by fluorescence microscopy. This is in the upper size range of bacterial genomes. showing that virtually all microscopically counted bacteria in this soil contain DNA. The total amount of DNA was about 90μg g-1 soil dry weight. © 1978.