Abstract

Nickel contamination leads to serious ecological and health risks, necessitating the need for sustainable remediation strategies. This study evaluated the nickel remediation potential of Enterobacter cloacae SK1, which exhibited a high minimal inhibitory concentration of 1100 ppm. Optimization experiments revealed a maximum nickel removal efficiency of 92.83% under optimal conditions of 48 h of contact time, 50 ppm initial nickel concentration, pH 7, temperature of 28°C, and 1.5% biomass concentration. Fourier transform infrared spectroscopy (FTIR) analysis indicated the involvement of functional groups, such as O–H, C–H, N–O, and C–N in nickel binding. Scanning electron microscope (SEM) analysis showed cell aggregation and shrinkage in nickel-exposed cells, while Transmission electron microscope (TEM) confirmed intracellular sequestration of nickel as electron-dense granules. Further, the cells were immobilized in alginate, agarose, and chitosan, and their removal efficiencies were compared. Alginate-immobilized cells achieved the highest removal efficiency (98.33%), compared with agarose (68.17%) and chitosan (75%). FTIR spectra of alginate-immobilized E. cloacae SK1 revealed the involvement of various functional groups (O–H, C–H, and N–H), while SEM showed increased surface damage following nickel exposure. In an in situ bioremediation experiment, alginate-immobilized cells removed 93.50% of nickel from contaminated soil compared to the native cells (91.24%). Genomic analysis identified resistance genes NiCoT, hupE, and mgtE, confirming the strain’s metal tolerance. Thus, these findings demonstrated that E. cloacae SK1 could be considered as a sustainable biological agent for mitigating nickel contamination in polluted environments.

Key words: Enterobacter cloacae SK1; Foundry soil; In-situ bioremediation; Nickel; RAST server.