Bioprotective mechanisms of Enterobacter sp. against arsenic, cadmium, and lead toxicity and its potential role in soil bioremediation

Heavy metal(loid) pollution in agricultural fields is a global menace, needing immediate effort to sustain crop production. Bioremediation, using microorganisms, reduces the toxicity and accumulation of these pollutants, safeguarding human health and the environment. The strain ACP-1 exhibits resistance to arsenic (As), cadmium (Cd), and lead (Pb), with a minimum inhibitory concentration of As500 +Pb1000 +Cd1500 mu g/ml. It was later identified as Enterobacter sp. through 16S rDNA sequence-based homology. The strain efficiently removed As, Pb, and Cd (92 %, 98 %, and 97 %, respectively) from a medium supplemented with mixed metals/metalloids (As100 +Pb200 +Cd300 mu g/ml). Varying adsorption capacity and efficiency were observed for both live and dead biomass of ACP-1 for As, Cd, and Pb. Distinct modes of extracellular adsorption along with the distribution pattern of As, Cd, and Pb in different cellular fractions during metal(loid)-microbe interactions were investigated. The strain also exhibited multiple plant growth-promoting traits and increased exopolysaccharide production (up to 320.83 mu g/ml) under multi-metal(loid) stress. The SEM-EDS and XRF studies indicated the presence of As, Cd, and Pb on the surface of ACP-1. Wherein, the FT-IR analysis showed the attachment of As, Pb, and Cd to different functional groups (such as amino, carboxyl, hydroxyl, alkene, and phosphate) located on the ACP-1's outer surface. XRD study revealed the formation of multiple As-, Cd-, and Pb-conjugated compounds on the cell surface during biosorption. The bioprotective mechanisms of ACP-1 against metal(loid)s played a crucial role in soil bioremediation, reducing As by 37.19 %, Cd by 42.84 %, and Pb by 21.5 % in sterile soil after 30 days.