Proceedings of the Insitute of Biology, Vol. VII, 2005, pp. THE BIOSOLUBILIZATION METALS OF THE PYRITE CONCENTRATES WITH CULTURES OF THIOBACILLUS FERROOXIDANS RESISTENT TO HIGH CONCENTRATIONS OF METALLIC IONS CARMEN CIŞMAŞIU The increasing pollution of the environment raised the interest towards the resistance of microorganisms to metals and the potential of using microorganisms, not only in ore leaching and detoxifying of the environments polluted with heavy metals. The sulphur wastes deposited in dumps with high concentrations of metallic ions have the capacity of generating acid and toxic waters. A special importance in using bacteria of the genus Thiobacillus in the metal solubilization processes from the acid mine draining is represented by adapting of these microorganisms to higher concentrations of metallic ions existent in those environments. High percentages of soluble pyrite were obtained using the P5 population of Thiobacillus ferrooxidans, which made the pyrite soluble in percentages of 87-92, which confirms its higher tolerance to Fe 3+ . The lowest percentages of solubilized pyrite (9.06-25.50%) were got in the presence of the Thiobacillus ferrooxidans B9 strain, this fact being correlated with the higher sensitivity of this strain to the presence of ferric iron in the environment. Key words: biosolubilization, pyrite, Thiobacillus ferrooxidans. INTRODUCTION The development of the biotechnological processes, based mainly on the activity of the acidophilic microorganisms, demonstrated their efficiencies in recovering metals from sulphur ores and mining drainage and in the bioremediation of the environment polluted with residual inorganic substances, like the heavy metals ions and their compounds (5, 8, 14). Biotechnology includes biohydrometallurgy (microbial leaching), metal bioaccumulation and bioprecipitation, metal biosorption and desulphurising of the fossil fuel. Biohydrometallurgy is a domain of great importance, being known that over 15% of the world production of copper is obtained from ores through microbial technology. This technology is based on the acidophilic chemolithotrophic microorganisms of the genus Thiobacillus, Leptospirillum, Sulfolobus, Metallosphaera, which grow on sulphur and iron from the sulphur ores, which they oxidate in the presence of atmospheric oxygen. Other acidophilic microorganisms accumulate and fix the metals, like the ones from the genera Acidiphilium, Alcaligenes, Sulfobacillus, thus participating in the formation of new metallic deposits (6, 11, 12).