(~K2opyright 1992 by The Humana Press Inc. All rights of any nature whatsoever reserved. 0273-2289/92/3435--0377502.00 Bioleaching of Low-Grade Copper Ores Using Thiobadllus ferrooxidans Scientific Note T. K. HAZRA, 1 M. MUKHERJEA, 1 AND R. N. MUKHERJEA *.2 i Department of Biochemistry, University College of Science, 35, Ballygunge Circular Road, Calcutta 700 019, India; and 2Process Engineering Design & Development Institute, AD. 161, Salt Lake City, Calcutta 700 064, India Index Entries: Thiobacillus ferrooxidans; copper ore, bioleaching; diethyl dithio carbamate; rusticyanin. INTRODUCTION Microbial leaching of copper ores using T. ferrooxidans is becoming increasingly important, and it is estimated to account for more than 10% of copper output throughout the world. However, although extensive studies are reported on bioleaching of metal sulfides using T. ferrooxidans, there is still limited understanding about the exact mechanism of the elec- tron transfer process involved. T. ferrooxidans, a gram-negative chemolithotropic bacterium, uses Fe 2§ as the sole source of energy and assimilates CO2 at the expense of energy derived from oxidative phosphorylation (1). Electron transport chain components involved in the oxidation of Fe 2§ reportedly include rusticyanin and several cytochromes of a and c types (2). Rusticyanin is a soluble type 1 blue copper protein present in the periplasmic space of the bacterium, consisting of a single polypeptide chain with one copper atom as a cofactor. It has a mol wt of 16,300 Da and has an absorption maxima at 597 (3). Diethyl dithiocarbamate [DEDC] reportedly shows antimicrobial activity against some organisms, such as E. coli, Klebsiella pneuraoniae, *Author to whom all correspondence and reprint requests should be addressed. Applied Biochemistry and Biotechnology 377 VoL 34/35, 1992