Rapid method for processing soil samples for polymerase chain reaction amplification of specific gene sequences.

Bacterial cells can be differentially separated from soil colloids on the basis of their buoyant densities. By using this principle, a modified sucrose gradient centrifugation protocol has been developed for separating bacterial cells from most of the soil colloids. Since the bacterial cell suspension still contained some colloidal soil particles, which inhibited polymerase chain reaction amplification, a new "double" polymerase chain reaction method of analysis was adopted for amplification of Tn5-specific gene sequences. This new protocol allowed rapid detection of small numbers (1 to 10 CFU/g) of bacterial cells present in soil samples.