A Mechanistic Insight in Cr (VI) Bioremediation by Bacillus spp. SSAU-2 Under Multi-Heavy Metal Contamination

Climate change has significantly contributed to high level of contamination of multi-pollutants in the environment. For instance, it increases the intensity of rainfall, leading to soil erosion and leaching of heavy metals, pesticides and other pollutants into the water bodies. Additionally, climate change intensifies both natural processes and anthropogenic activities resulting in the widespread release and dispersal of heavy metals (HMs) and other pollutants, posing great risk to environment and human health. Cr (VI) is the most hazardous metal contaminant in the ecosystem. In the environment, it often coexists with other heavy metal such as Fe (III), Zn (II), Pb (II), Hg (II), Cd (II) and Cu (II) which interferes with the Cr (VI) removal strategies and significantly influence the efficiency of bioremediating microbes. In this study, the Cr (VI) removal potential of the novel microbe Bacillus sp. SSAU-2 was explored in the presence of multi-heavy metal contaminations in various combinations. The tolerance against HM of the SSAU-2 was analyzed with minimum inhibition concentration (MIC) study and the mechanism was observed by analyzing the various types pf Siderophore production in the presence of HM. Revealed that the SSAU-2 exhibits multi-heavy metal tolerance, with the following MIC order Pb (II) > Fe (III) > Cu (II) > Cr (VI) > Zn (II) > Cd (II) > Hg (II). The presence of Zn (II), Fe (III) and Cu (II) acted as positive inducers, enhancing its growth and Cr (VI) removal efficiency. Although SSAU-2 demonstrates remarkable resistance to most heavy metals, it is highly susceptible to Hg (II) and Cd (II). However, Hg (II) proved to be the most toxic, reducing the Cr (VI) removal efficiency from 83 to 32% even at a concentration of 0.1 ppm concentration. The mechanism underlying its multi-heavy metal tolerance is linked to the production of siderophore, particularly catechol-type siderophore. Thus, this study highlights the potential of SSAU-2 as a robust microbe, capable of sustaining its Cr (VI) removal ability even in the presence of multiple heavy metals. Therefore, this microbe can tackle the adverse climate change phenomenon and environmental pollution altogether.