The
Role of Microorganisms in Biosorption of Toxic
Metals and Radionuclides
Christopher White,
Simon C. Wilkinson & Geoffrey M. Gadd*
Department of Biological Sciences, University
of Dundee,
Dundee DDl 4HN, UK
International
Biodeterioration & Biodegradation (1995) 17-
40
Abstract
A
multiplicity of physico-chemical and biological
mechanisms determine the removal of toxic metals,
metalloids and radionuclides from contaminated
wastes. Physico-chemical mechanisms of removal,
which may be encompassed by the general term 'biosorption",
include adsorption, ion exchange and entrapment
which are features of living and dead biomass
as well as derived products. In living cells,
biosorption can be directly and indirectly influenced
by metabolism. Metabolism-dependent mechanisms
of metal removal which occur in living microorganisms
include metal precipitation as sulphides, complexation
by siderophores and other metabolites, sequestration
by metal-binding proteins and peptides, transport
and intracellular compartmentation. In addition,
transformations of metal species can occur resulting
in oxidation, reduction or methylation. For metalloids
such as selenium, two main transformation mechanisms
are the reduction of oxyanions to elemental forms,
and methylation to methylated derivatives, which
are volatilized. Such mechanisms are important
components of natural biogeochemical cycles for
metals and metalloids as well as being of potential
application for bioremediation.
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