Removal of cadmium through biomineralization using halophilic and ureolytic bacteria under saline conditions

Abstract

Heavy metal pollution poses an immense challenge to humanity owing to its severe toxic effects on living beings. This study investigates the bioremediation potential of the urease-hydrolyzing and halophilic bacterium Bacillus paramycoides- MSR1 to reduce the toxicity of cadmium (Cd) in the environment under salt stress through microbially induced calcium carbonate precipitation (MICCP). The enzymatic activity of urease and calcium carbonate (CaCO₃) precipitation was studied under different concentrations of salt stress (0%, 3.5%, 5%, 7.5%, 10%, 15%) and maximum urease activity of 735.7 U/ml was recorded at 5% salt stress. The urease activity and CaCO₃ precipitation decreased with increasing Cd toxicity (0, 10, 20, 30, 40, 50, and 60 μM). The maximum concentration of Cd endured by bacteria was determined by IC₅₀ value and the minimum inhibitory concentration of Cd was recorded as 9.86 μM under 5% stress. Atomic absorption spectroscopy results revealed that Cd removal was as high as 90.3% under 5% salt stress. Microstructural analysis through FE-SEM revealed the surface topography of carbonate crystals as rhombohedral, whereas EDS confirmed the presence of CaCO₃ and Cd in the bio-precipitates. These results suggest that MICCP is a potential, environmentally safe, low-cost technique and an excellent alternative to conventional heavy metal removal strategies from the environment.