PRESERVATION AND REACTIVATION OF IRON-OXI DIZING BACTERIA INVOLVED INTHE BIOLEACHING OF CONTAMINATED SOILS

Cultures of Thiobacillus ferrooxidans, widely used in various bioleach ing processes, are usually maintained by time consuming serial transfe rs in a liquid medium at regular short intervals. Moreover, no preserv ation methods were previously investigated for indigenous iron-oxidizi ng bacterial communities. Hence, two simple methods of preservation we re tested for acclimatized acidophilic microflora mainly composed of i ron-oxidizing bacteria and of heterotrophic acidophilic bacteria isola ted from three contaminated soils: (i) storage in soil suspension at 4 degrees C and (ii) storage at -20 degrees C with various cryoprotecti ve agents. After 4 and 8 months, the activity expressed in terms of ox ide-reduction potential increase and pH drop was checked. As well, hea vy metals (Zn, Cu, Mn) extraction ability of preserved cultures was te sted. It was found that storage in soil suspension at 4 degrees C was the best method of preservation for the three iron-oxidizing bacterial communities tested. After revival, the activity of the three acclimat ized microflora was intact after 8 months of storage at 4 degrees C in soil suspension. The bioleaching ability of preserved microflora was fully retained. Cultures stored at -20 degrees C during 4 months with cryoprotective agents could not be revived.