Published online by Cambridge University Press: 22 August 2009
INTRODUCTION
Toxic heavy metals and metalloids constitute an international pollution problem that not only impacts public health but also is of environmental and economic importance. Prokaryotes with the physiological activity of sulphate reduction are found in a number of environmental sites containing toxic metals and these microorganisms have developed several different strategies for resistance to toxic elements. Some bacteria have developed detoxification strategies that are potentially useful for bioremediation. Since sulphate-reducing bacteria (SRB) are found in a large number of contaminated sites containing toxic metals, it is apparent that these organisms have a functional defence system that enables them to persist and even grow under metal stress. The enzymatic metal reduction by SRB offers an alternative to chemical processes to remediate environments containing redox-active toxic metals and metalloids. While Hockin and Gadd discuss in Chapter 14 the bioremediation activities of sulphate-reducing bacteria, this chapter focuses on the enzymatic processes associated with metal reduction. We review results obtained with isolated proteins and discuss the potential of sulphate-reducers by reviewing putative proteins found in their genomes. Reference is made to putative genes present in Desulfovibrio (D.) vulgaris strain Hildenborough (Heidelberg et al., 2004), D. desulfuricans strain G20 (http://www.jgi.doe.gov), Desulfotalea (Des.) psychrophila (Rabus et al., 2004) and Archaeoglobus (A.) fulgidus (Klenk et al., 1997).
ENZYMATIC ACTIVITIES INVOLVING REDOX-ACTIVE ELEMENTS
The detoxification of an environment arising from SRB reductions is considered by many as an important event for bioremediation of various polluted environments In addition to precipitation of metals by biogenic hydrogen sulfide, the SRB are highly capable of reducing many soluble redox-active elements.
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