Bioremediation of Toxic Metals for Protecting Human Health and the Ecosystem

Aminur Rahman (2016): Bioremediation of Toxic Metals for Protecting Human Health and the Ecosystem. Örebro Studies in Life Science 15. Heavy metal pollutants, discharged into the ecosystem as waste by anthropogenic activities, contaminate drinking water for millions of people and animals in many regions of the world. Long term exposure to these metals, leads to several lethal diseases like cancer, keratosis, gangrene, diabetes, cardio-vascular disorders, etc. Therefore, removal of these pollutants from soil, water and environment is of great importance for human welfare. One of the possible eco-friendly solutions to this problem is the use of microorganisms that can accumulate the heavy metals from the contaminated sources, hence reducing the pollutant contents to a safe level. In this thesis an arsenic resistant bacterium Lysinibacillus sphaericus B1CDA, a chromium resistant bacterium Enterobacter cloacae B2-DHA and a nickel resistant bacterium Lysinibacillus sp. BA2 were isolated and studied. The minimum inhibitory concentration values of these isolates are 500 mM sodium arsenate, 5.5 mM potassium chromate and 9 mM nickel chloride, respectively. The time of flight-secondary ion mass spectrometry and inductively coupled plasma-mass spectroscopy analyses revealed that after 120 h of exposure, the intracellular accumulation of arsenic in B1-CDA and chromium in B2-DHA were 5.0 mg/g dwt and 320 μg/g dwt of cell biomass, respectively. However, the arsenic and chromium contents in the liquid medium were reduced to 50% and 81%, respectively. The adsorption values of BA2 when exposed to nickel for 6 h were 238.04 mg of Ni(II) per gram of dead biomass indicating BA2 can reduce nickel content in the solution to 53.89%. Scanning electron micrograph depicted the effect of these metals on cellular morphology of the isolates. The genetic composition of B1-CDA and B2-DHA were studied in detail by sequencing of whole genomes. All genes of B1-CDA and B2-DHA predicted to be associated with resistance to heavy metals were annotated. The findings in this study accentuate the significance of these bacteria in removing toxic metals from the contaminated sources. The genetic mechanisms of these isolates in absorbing and thus removing toxic metals could be used as vehicles to cope with metal toxicity of the contaminated effluents discharged to the nature by industries and other human activities.