Sampling soil microfloras: Optimization of density gradient centrifugation in percoll to separate microorganisms from soil suspensions

Suspensions of non-filamentous microorganisms and clay were prepared by dispersing soil with an ion-exchange resin, sieving, elutriation and ultrafiltration. Cells were separated from clay by density gradient centrifugation in linear gradients of Percoll (limiting densities 1.101 and l.139 gcm⁻³). By fractionating the density gradient, the mixed population could be separated into components of differing density. Percoll could be separated from microorganisms by gel chromatography on columns of Sephacryl S-1000 or centrifugation after dilution.