How do bacteria interact with minerals?

Over the last 35 years, there has been a debate concerning the interaction of iron- and sulfur-oxidizing bacteria and sulfide minerals. Two basic positions are held. The proponents of the direct mechanism argue that the bacteria possess a specific biological mechanism to degrade the mineral and thereby gain energy directly from the sulfide mineral. On the other hand, the proponents of the indirect mechanism argue that it is the ferric ions in solution that dissolve the mineral, and the bacteria gain their energy requirements from regenerating the ferric ions. The indirect mechanism undoubtedly occurs, but proponents of the direct mechanism argue that it is not the dominant route. In other words, the debate hinges on the kinetics of each of these possible paths. The evidence presented in the published literature both for and against each of these mechanisms has been critically examined. Arguments based on stoichiometry, bacterial attachment or observations of the mineral surface cannot resolve this debate. Since the critical factor is the kinetics of each proposed path, only kinetic studies can resolve the debate. Based on the evidence of the kinetic studies that were performed, a resolution to the debate is suggested. (C) 2003 Elsevier B.V. All rights reserved.