The maintenance of free-living amoebae by cryopreservation.

We have successfully cryopreserved free-living amoebae in order to maintain them feasibly under the conditions in our laboratory. The viability of trophozoites was higher when frozen by slow cooling (overall 0.7 degree C/min) than by fast cooling (overall 1.3 degrees C/min). Glycerol and dimethylsulfoxide at the final concentration of 7.5% each was used for cryopreservation of free-living amoebae trophozoites. The survival rate was 2-39% after storage in the liquid nitrogen for 60 days. Gross cultural or morphological changes were not noted in trophozoites thawed from frozen suspensions.