Metals, minerals and microbes: geomicrobiology

and bioremediation

Geoffrey Michael Gadd

Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee

DD1 5EH, UK

Microbes play key geoactive roles in the biosphere, particularly in the areas of element

biotransformations and biogeochemical cycling, metal and mineral transformations,

decomposition, bioweathering, and soil and sediment formation. All kinds of microbes, including

prokaryotes and eukaryotes and their symbiotic associations with each other and ‘higher

organisms’, can contribute actively to geological phenomena, and central to many such

geomicrobial processes are transformations of metals and minerals. Microbes have a variety of

properties that can effect changes in metal speciation, toxicity and mobility, as well as mineral

formation or mineral dissolution or deterioration. Such mechanisms are important components of

natural biogeochemical cycles for metals as well as associated elements in biomass, soil, rocks

and minerals, e.g. sulfur and phosphorus, and metalloids, actinides and metal radionuclides. Apart

from being important in natural biosphere processes, metal and mineral transformations can have

beneficial or detrimental consequences in a human context. Bioremediation is the application of

biological systems to the clean-up of organic and inorganic pollution, with bacteria and fungi

being the most important organisms for reclamation, immobilization or detoxification of metallic

and radionuclide pollutants. Some biominerals or metallic elements deposited by microbes have

catalytic and other properties in nanoparticle, crystalline or colloidal forms, and these are relevant

to the development of novel biomaterials for technological and antimicrobial purposes. On the

negative side, metal and mineral transformations by microbes may result in spoilage and

destruction of natural and synthetic materials, rock and mineral-based building materials (e.g.

concrete), acid mine drainage and associated metal pollution, biocorrosion of metals, alloys and

related substances, and adverse effects on radionuclide speciation, mobility and containment, all

with immense social and economic consequences. The ubiquity and importance of microbes in

biosphere processes make geomicrobiology one of the most important concepts within

microbiology, and one requiring an interdisciplinary approach to define environmental and applied

significance and underpin exploitation in biotechnology.