Indian Ocean manganese nodules offer a lucrative resource for valuable strategic metals like Cu, Co and Ni. A novel bio-leaching process to recover these metals in presence of organic reductants from the nodules at near neutral pH and ambient temperature is presented in this paper. The cell-free growth supernatant of a marine microorganism isolated from the nodules was employed in bioleaching studies of the nodules. The organic metabolites produced during growth of the microorganism, play a primary role in the leaching process by reduction of oxides and/or complexation of the transition metals. Around 40% cobalt and 25% of Cu and Ni were recovered in the leach liquor at near neutral pH values in about two hours, indicating that, metabolites preferentially leach cobalt compared to copper and nickel. Chemical leaching tests were also carried out with organic reactants under similar conditions and the recovery of transition metals was compared with that of leaching with growth supernatant alone. Finally, when growth supernatant was supplemented with certain organic reactants like ascorbic acid, 60-70% recovery of Cu, Co and Ni was obtained in solution within half an hour. (C) 2003 Elsevier Science Ltd. All rights reserved.