Cadmium In Microorganisms

Cadmium is present on the earth’s crust as heavy metal and its exposure in the environment is a very big challenge to environmentalist because cadmium is non-degradable in nature. In environment cadmium transfers from one trophic level to another and finally accumulated in human with toxic effects. There is an emerging need to remove the cadmium from the environment. Microbes are very helpful in this area to remediate the cadmium from the environment. Microorganisms used biotransformation and adsorption mechanisms for regulation of translocation of heavy metals. In present time, many research has been done on the toxicity of cadmium in microorganisms. Microorganisms release many types of organic and inorganic substances by which they can detoxify

In some bacteria, cadmium enters in to cell by few manganese uptake systems (Burke and Pfster, 1986; Tynecka and Malm, 1995) and in plants cadmium is taken up via the calcium uptake system (Clemens et al., 1998). Resistance property in bacteria against cadmium metal is developed due to cadmium efflux. Cadmium resistance increased because of the amplification of the metallothionein locus (Gupta et al., 1993) and removal of it decreases resistance (Gupta et al., 1993; Turner et al., 1993; Turner et al., 1995). The smtB repressor of microorganisms controls a zinc-transporting P-type ATPase (Thelwell et al., 1998) and also regulates the function of the metallothionein gene, smtA (Huckle et al., 1993; Turner et al.,

Under metal-stressed environment, for survival, bacteria have evolved various mechanisms by which they can immobilize, mobilize or transform metals and makes them inactive to tolerate the uptake of heavy metal ions (Nies, 1999). Such mechanisms are as (Tabak et al., 20050 exclusion (the metal ions are kept away from the target sites) (Ahemad et al., 2009) extrusion (the metals are pushed out of the cell through chromosomal/plasmid mediated events) (Ahemad and Khan, 2011) accommodation (the metal binding proteins form complex with metals) (Umrania, 2006; Nies and Silver, 1995) or other cell components (Vidali, 2001) bio-transformation toxic metal is reduced to less toxic forms and (Kamaludeen et al., 2003) methylation and demethylation. These defense mechanisms permit microorganisms to function metabolically in heavy metals polluted environment. The Cd-efflux ATPase mechanism is involved in cadmium resistance in Gram-positive