FIG. 1.

Equilibrium centrifugation of DNA extracted from soil that oxidized ¹²CH₄ (a) or ¹³CH₄ (b). CsCl-ethidium bromide (100 μl at 10 mg ml⁻¹) density gradients were centrifuged at 265,000 × g for 16 h, and DNA was visualized with long-wavelength (365-nm) UV light. The positions of the ¹²C-DNA (indicated by “[”) and ¹³C-DNA (indicated by “]”) fractions collected after primary ultracentrifugation are indicated. Bar, 1 cm.