Resistance to metals

Although some metal cations and oxyanions can serve as electron acceptors for growth under anaerobic conditions, reduction may also take place gratuitously, and these reductases have been characterized in a number of organisms. Reduction has been implicated in resistance to metal cations and metalloid oxyanions, which are discussed in Part 4 of this chapter. 

It is therefore clear that care should be exercised in assigning metallothioneins to a cardinal role in conferring resistance to metals. 

Resistance to heavy metals including Hg may be mediated by plasmid-borne genes. Further discussion of resistance to metal cations and metalloid anions is given in Chapter 3, Part 4. 

Although knowledge on the biodegradation of these compounds is sparse, a number of them are important in industrial processes. Formation of methylated derivatives may take place in metals and metalloids belonging to groups 15 and 16 of the periodic table, and a few of group 14. These have been discussed in a critical review (Thayer 2002) and in Chapter 3, Part 4, and they have been noted in the context of the bacterial resistance to metals and metalloids. Since carbon monoxide has been considered as an organic compound (Chapter 7, Part 1), it is consistent to make brief comments on metal carbonyls. 

Polyurethanes provide a large package of chemical resistance to metals within the operating temperature of the polymer. By careful selection, alloys can be used to provide the desired chemical resistance, but normally at a cost disadvantage. 

For smaller particle sizes ( 1,000 microns), polyurethanes provide a superior erosive wear resistance to metals at most normal velocities of up to 20m/s. Outside these limits, the materials need to be evaluated in a manner that is as close to real conditions as possible. 

Levinton, J.S., Suatoni, E., Wallace, W., Junkins, R., Kelaher, B., and Allen, B.J. (2003) Rapid loss of genetically based resistance to metals after clean-up of a Superfund site. Proc. Natl. Acad. Sci. USA. 100, 9889-9891. 

Bruins, R.M., Kapil, S., and Oehme, S.W. 2000. Microbial resistance to metal in the environment. Ecotoxicology and Environmental Safety, 45 198-207. 

Sarret, G., Manceau, A., Cuny, D. et al. (1998). Mechanisms of lichen resistance to metallic pollution. Environmental Science and Technology, 32, 3325-30. 

It is the aqueous dispersion of a fatty acid salt and it is resistant to metal salts. It can be used for all types of fibre, but is recommended mainly for cellulosic textiles. 

Plasmids are present in most strains of T. ferrooxidans, although these have not been implicated in resistance to metals, apart from resistance to UOi" (84,85). These plasmids could serve as vectors to carry genes back into T. ferrooxidans cells. 

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