Assimilatory and dissimilatory processes of microorganisms affecting metals in the environment

Microorganisms use a variety of strategies to extract trace metals from minerals. In addition to meeting metabolic needs, these microbe–mineral interactions affect mineral weathering and element cycling. Evidence of these interactions in the geological record could be used as "biosignatures" to detect the evolution of microbial metal metabolism over geological time. Here, we review the use of inductively coupled plasma-mass spectrometry (ICP-MS) to investigate trace metal extraction from minerals by microorganisms. These metals may be taken up, or assimilated, by the microorganisms for use in enzymes and cellular components. Alternatively, in dissimilatory processes, extracted metals remain outside the cell where they are reduced or oxidized to remove or provide electrons for cellular energetics. Data obtained by ICP-MS and complementary methods demonstrate changes in metal content within cells, as well as in the surrounding media and minerals, leading to a greater understanding of microbe–mineral interactions. The development and application of new ICP-MS technology, such as high resolution ICP-MS and, more recently, multiple-collector ICP-MS, continues to add to our understanding of these processes.