Heavy metal incorporation in bacteria and its environmental significance

Heavy metals are a relatively new class of contaminants. Bacteria play a very important role in decomposition processes in ecosystems. This review intends to establish the pathways of metal entry into bacteria and their toxicological relevance. The heavy metal-bacteria interactions are well known to occur at extracellular levels, at the bacterial surface or intracellularly. At the extracellular level, the role of microorganisms in metal mobilization and inmobilization, and the release of low molecular weight organic compounds (siderophores) with high affinity for metals have been established. Interactions of a particular metal with the bacterial surface vary with bacterial strain, as metals interact with negatively - charged specific groups. At intracellular level, enzimatic transformations and specific protein synthesis (metalothioneins) can occur after metal accumulation. In general, heavy metal-bacteria interactions occur in serial events that begin outside the cell and end intracellularly. These events may or may not occur in sequence and depend on the bacterial strain, the metal species and the cell compartment considered.