Bioremediation nature of heavy metals can be changed

Bioremediation of heavy metals by microorganismsSoil contamination is one of the major environmental problems across the world, one of the soil contaminant heavy metal is of major concern. In past heavy metals were limited to industrial and mining sites only but today it is knocking at our door. Heavy metals has now became an existential threat to the biotic factor of the ecosystem as it interact with various biochemical pathways that takes place inside microorganisms, plants, animals and humans ( Collins and Stotzky, 1989 ). One of the alarming fact about the heavy metals pollution is that it can’t be degraded by biological, physical or chemical means like the organic pollutants ( Knox et al, 2000 ) however the chemical nature of heavy metals can be changed by reduction or oxidation ( Garbisu and Alkorta, 1997 )but the elemental nature resist change, making heavy metals  persistent to degradation and thus remain in soil for a long period after their introduction. Soil can become contaminated by toxic metalloids and heavy metals accumulation through natural weathering of parent material and emissions from various industries using heavy metals as a raw material such as lead from batteries manufacturing industries, lead (pb) containing paints, heavy metals based pesticides such as baurdeax mixture ( copper sulphate ), sewage sludge, animal manures and fertilizers ( Raskin et al, 1994 ).These are the most common toxic heavy metals found at contaminated sites: Lead (Pb), Chromium (Cr), Arsenic (As), Zinc (Zn), Cadmium (Cd), Copper (Cu), Mercury (Hg), and Nickel (Ni). These toxic heavy metals can’t be degraded however their  bioavailability can be reduced by a variety of physical, chemical and biological methods such as coagulation and flocculation, ion exchange,  chemical precipitation,  electrochemical treatment,  membrane filtration, phytoremediation, phytostabilization, phytoextraction, and bioremediation etc we will only focus on bioremediation that primarily involve the use of microorganisms in this paper (assignment). Currently it is the main focus of researchers trying to find out methods that are rapid, effective and cheap to remove toxic heavy metals from environment or atleast reduce it to a harmless or non-bioavailable form using microorganism ( Diels, 1993; Gadd, 1992 ) Better understanding of the nature of toxic heavy metals and The isolation of heavy metal resistant microorganisms and the understanding of the mechanisms they use in order to remove this kind of pollutants may contribute to the development of improved bioremediation processes ( Vargas et al, 2001 ).Bioremediation:Various techniques have been developed to tackle the problem of heavy metal pollution each of these techniques have their own advantages and disadvantages some of the common physical and chemical techniques ( Vidali, 2001 ) are mentioned earlier.Bioremediation has evolved as a promising, sustainable, rapid and low cost alternate to the  mentioned physical and chemical techniques. The term Bioremediation is a universal stereotype including those processes and actions that takes place so that to biotransform a selected environment, that is already changed by toxic pollutants, to its initial form is known as bioremediation ( Helena, 2003; Asha et al, 2013 ). Bioremediation uses predominantly microbial processes or microorganisms  such as yeast etc to degrade or convert environmental pollutants into less toxic or harmless  substitutes ( Kumar et al, 2011 ). In bioremediation microorganisms use the pollutants as source of energy ( Asha et al, 2013 ) preciselyspeaking it is mainly concerned with the use of “microorganisms” to degrade pollutants. However in this context, phytoremediation is characterized as the use of green plants to take off environmental pollutants or to reduce them to less toxic or harmless form ( Cunningham and Berti, 1993; Raskin et al, 1994, 1997; Salt et al, 1995, 1998; Asha et al, 2013 ). Phytoremediation  is developed