Sequestration of mercury and cadmium by a heavy metals' tolerant Bacillus cereus strain JS-3: a microbial preparedness for terrestrial and anthropogenic hazards

Abstract

A large number of heavy metals are discharged in the form of industrial effluents into the soil and natural water bodies beyond the permissible limits. Accumulation of bio-available forms of these hazardous elements in the natural sites poses both environmental and human health implications throughout the globe. In the present study, a bacterial strain JS-3 has been explored toward its tolerance for different heavy metals along with sequestration and transformation of mercury and cadmium. Strain JS-3 was characterized morphologically, physiologically, and biochemically followed by 16S rRNA homology analysis and identified as Bacillus cereus. The results highlight that isolate has a remarkable tolerance (up to 20 µg/g as an active ingredient) toward almost all heavy metals such as Pb, Cd, Ni, As, Hg and Se. After acclimatization in first 24 hours, almost comparable growth has been observed in control and mercury supplemented Tryptone Soya Broth (TSB) while a significant impact on the growth was observed in cadmium supplemented TSB. After 96 hours, almost 80% of the mercury and 70% cadmium has been sequestered in the biomass supplemented with 25 µg/g of these metal salts with a decrease in sequestration with increase in initial concentration of metals has been observed. SEM and EDX analysis further confirmed the accumulation of these metals in the biomass. XRD-analysis of the biomass revealed no characteristic peak associated with the crystalline nature of the mercuric chloride and cadmium chloride but it ensures transformation of these salts into the amorphous material within the bacterial cells.