Review
Bioremedial potential of microbial mechanisms of metal mobilization and immobilization

https://doi.org/10.1016/S0958-1669(00)00095-1Get rights and content

Abstract

Microorganisms play important roles in the environmental fate of toxic metals and radionuclides with a multiplicity of mechanisms effecting transformations between soluble and insoluble forms. These mechanisms are integral components of natural biogeochemical cycles and are of potential for both in situ and ex situ bioremedial treatment processes for solid and liquid wastes.

Introduction

The mechanisms by which microorganisms effect changes in metal speciation and mobility are fundamental components of biogeochemical cycles for metals, as well as all other elements including carbon, nitrogen, sulfur and phosphorus, with additional implications for plant productivity and human health [1••]. Almost all metal–microbe interactions have been examined in the context of environmental biotechnology as a means for removal, recovery or detoxification of inorganic and organic metal or radionuclide pollutants 2, 3, 4••, 5••. Although much research is laboratory based, there have been many developments to pilot/demonstration scale, with some processes apparently in successful commercial operation. It should also be noted that metal removal/transformation processes are intrinsic though less appreciated components of traditional means of water/sewage treatment as well as reed bed, lagoon and wetlands technologies 4••, 6. Molecular and genetic analysis is now furthering our understanding of microbial metal metabolism, including those aspects that have potential in biotechnology 7••, 8••. This review details recent advances in understanding of the most important mechanisms of microbial metal transformations within the contexts of bioremediation and environmental biogeochemistry.

Section snippets

Leaching

Leaching of mineral ores by acidophilic sulfur-oxidizing bacteria is an established bioindustry and although most interest arises from a hydrometallurgical perspective, leaching of contaminating metals from soils and other matrices is also possible [9••]. In fact, bioleaching using elemental sulfur as substrate can be better than sulfuric acid treatment for metal solubilization from contaminated aquatic sediments [10]. Iron- and sulfur-oxidizing bacteria, Thiobacillus ferrooxidans and

Biosorption

Biosorption encompasses those physico-chemical mechanisms by which metal species, radionuclides and so on, are removed from aqueous solution by microbial biomass or products. The approach can be multidisciplinary as the basic nature of experimentation is attractive to biologists, chemists and engineers, although inadequate dialogue between such groups has lead to considerable superficiality and duplication in the literature. It has also lead to the submersion of many other metal accumulation or

Conclusions

Mechanisms of microbial solubilization and immobilization of metal(loid)s, radionuclides and related substances are of clear potential for bioremediation, with some processes being integral to the operation of several successful in situ and ex situ processes. Although biosorption research is rather introverted with little recent development in an industrial context, work on metal leaching from contaminated matrices, metal(loid) transformation and bioprecipitation is leading to ‘field’

Update

Developments of relevance to this topic, published since submission of the manuscript, have occurred in several areas including biosorption, alkylation and reduction.

In an attempt to create a metal-capturing system for use in bioremediation, a peptide library was screened for binding to ZnO. By engineering a structural component of the fimbrae of E. coli to display a random peptide library, metal-chelating bacteria were isolated. Sequences responsible for Zn adherence were identified and

Acknowledgements

The author gratefully acknowledges financial support for his own work described from the Biotechnology and Biological Sciences Research Council (SPC 02812, SPC05211, BSW 05375) and the Royal Society.

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

  • • of special interest

  • •• of outstanding interest

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