The presence of radionuclides and heavy metals in our surroundings has become the most serious environmental concern. These contaminants or pollutants fail to degrade on their own over time and must be removed or neutralized. Microorganisms act as natural catalysts in the process of transformation of toxic metals into non-toxic ones. This is why there is an increased interest in the understanding of microbiological processes which help in remediation of these toxic wastes from the environment (Francis 1990).
Microorganisms basically work by mobilization and immobilization of heavy metals and radioactive wastes. Mobilization include processes such as methylation of wastes and thus making them volatile substances, chelation of metals to…show more content… This product is also found to be readily acted upon by a variety of degrading bacteria, algal species and fungal species also (Gadd 1996), (Karlson et al. 1993).
b) Autotrophic Leaching:
The chemolithic and acidophilic bacteria help in carrying out the autotrophic leaching of metals. They function by fixing carbon-di-oxide and obtaining energy from the oxidation of ferrous ions or reduced sulphur compounds, and form Fe(III) or H2SO4 as the end products (Bosecker 1997). The microorganisms involved in this process are Thiobacillus thioxidans, Thiobacillus ferroxidans, Leptospirillum ferroxidans (Ewart and Hughes 1991).
Also the production of sulphuric acid by Thiobacillus species is a form of bioremediation of sewage wastes. This technique has been used to remediate the problems of heavy metal contaminated soil, water, sewage etc.
c) Heterotrophic Leaching:
Heterotrophic metabolism can also account for leaching as it can cause the release of proton or organic acids (Burgstaller and Schinner 1993). For eg., Uranium reacts with chelating anion like citrate and form very stable Uranium- citrate complexes (Borkowski et al. 1997).
Now, many microorganisms such as bacteria or fungi are able to act upon these metal-chelate complexes and thus form products which are non- toxic to environment.