Mercury resistant bacillus cereus isolated from the Pulicat Lake Sediment, North Chennai Coastal Region, South East India

Among the 90 naturally occurring elements, 21 are non-metals, 16 are light metals and the remaining 53 (with As including) are heavy metals. In these 53 heavy metals not all elements are toxic: some are required for catalyzing key reactions or for maintaining the protein structure, to maintain the osmotic balance and to catalyze several biochemical reactions. Hence, based on the physiological point of view, the metals are classified into three groups namely (i) Essential and basically non-toxic e.g., Ca and Mg, (ii) Essential but harmful under higher concentration e.g., Fe, Mn, Zn, Cu, Co etc. and (iii) Toxic metals e.g., Hg and Cd (Valls and Lorenzo, 2002).