Fe (III)-mediated enhancement of Bacillus sp. SSAU2 resilience against Hg (II) toxicity and restoration of its Cr (VI) removal efficiency in a mercury-contaminated environment.

Industrialization and urbanization have led to increasingly severe impacts on environmental sustainability, through the release of heavy metals into the environment. This study employed a sustainable approach involving metallic treatment and an acclimatization process to enhance the resilience of the microbe Bacillus sp. SSAU2 against Hg (II) toxicity. The findings revealed that acclimatization at 0.05 ppm Hg (II) and 0.2 ppm Fe (III) treatment significantly improved Hg (II) tolerance, with the 300% increase in the Minimum inhibitory concentration (MIC) achieved through a composite treatment combining metal treatment and acclimatization. FTIR analysis indicated that the composite treatment exhibits unique functional groups and provides evidence of the direct involvement of Fe-nanoparticles, a finding further corroborated by UV-visible studies and SEM micrographs. The enhanced binding observed post-treatment, along with a shift toward multilayer adsorption was analyzed using isotherm models. Meanwhile, kinetics studies revealed that Hg (II) exposure altered the Cr (VI) removal kinetics of SSAU2 from second-order to first-order. Thermodynamic analysis indicated that while Hg (II) toxicity drives the system towards negative entropy and exothermic reactions, the composite treatment uniquely maintained positive entropy and endothermic behavior across all Cr (VI) levels, suggesting the involvement of resistance mechanisms. By the mechanism, this work presents a novel method for addressing co-contamination and the challenges posed by toxic compounds in the environment.