separation of bacteria from soil particles according to sedimentation velocities was first described by Faegri et al. this method is based on two successive centrifugation: first a low speed centrifugation ranging from 500 x g to 1000 x g lasting 2-15 min, respectively, in order to remove (sediment) soil debris, fungal mycelia and heavy soil particle. Optimal conditions for low-speed centrifugation is a compromise between cell recovery efficiency and elimination of contaminating material. A subsequent high-speed centrifugation of the cell-containing supernatant produces the bacterial fraction. Chains and clusters of bacteria and bacteria attached to soil particles might be easily lost during the first centrifugation. Holben et al. established that approximately 10 % of the total bacteria present in the soil were released per rount of homogenization-separation. According to these authors, the bacterial fraction released after a single round is apparently as representative of the total bacterial population as after multiple rounds. Several rounds of extraction may, however,greatly improve total cell recovery.