In vitro and in silico Studies Reveal Bacillus cereus AA-18 as a Potential Candidate for Bioremediation of Mercury-Contaminated Wastewater

Abstract

Mercury (Hg) pollution is a worldwide problem and increasing day by day due to natural and anthropogenic sources. In this study, mercury-resistant (HgR) bacterial isolates were isolated from industrial wastewater of Ittehad Chemicals Ltd., Kala Shah Kaku, Lahore, Pakistan. Out of 65 bacterial isolates, five isolates were screened out based on showing resistance at 30–40 μg/ml against HgCl2. Selected Hg-resistant bacterial isolates were characterized as Bacillus subtilis AA-16 (OK562835), Bacillus cereus AA-18 (OK562834), Bacillus sp. AA-20 (OK562833), Bacillus paramycoides AA-30 (OK562836), and Bacillus thuringiensis AA-35 (OK562837). B. cereus AA-18 showed promising results in the resistance of HgCl2 (40 μg/ml) due to the presence of merA gene. Scanning electron microscopy (SEM) analysis of immobilized B. cereus AA-18 showed the accumulation Hg on the cell surface. The inoculation of immobilized B. cereus AA-18 remediated 86% Hg of industrial wastewater up to 72 h at large scale (p < 0.05). In silico analysis showed structural determination of MerA protein encoded by merA gene of B. cereus AA-18 (OK562598) using ProtParam, Pfam, ConSurf Server, InterPro, STRING, Jpred4, PSIPRED, I-TASSER, COACH server, TrRosetta, ERRAT, VERIFY3D, Ramachandran plot, and AutoDock Vina (PyRx 8.0). These bioinformatics tools predicted the structural-based functional homology of MerA protein (mercuric reductase) associated with mer operon harboring bacteria involved in Hg-bioremediation system.

Bioremediation of mercury contaminated soil and water: A review

“…Encoded by periplasmic protein (merP), merA and merB, as well as several inner Overexpressing merB gene Degrade MeHg to more than 81.6% in a culture medium under anoxic and oxic conditions Q. Yang et al (2023) membrane proteins such as merT, merC, merE, merF and merG, aid in transporting Hg(II) into or out of the cytoplasmic membrane (Amin et al, 2022;Amin & Latif, 2017). The mercury transporter proteins (merC, merP, merE and merT) are responsible for the transportation of Hg(II), whereas the cytoplasmic reductase encoded by the merA gene is accountable for the conversion of Hg(II) into Hg(0) (Giri et al, 2014).…”

“…Organomercury lyase, encoded by merB, catalyses protonolytic breakdown of C‐Hg bonds in organo Hg compounds. Encoded by periplasmic protein (merP), merA and merB, as well as several inner membrane proteins such as merT, merC, merE, merF and merG, aid in transporting Hg(II) into or out of the cytoplasmic membrane (Amin et al, 2022; Amin & Latif, 2017). The mercury transporter proteins (merC, merP, merE and merT) are responsible for the transportation of Hg(II), whereas the cytoplasmic reductase encoded by the merA gene is accountable for the conversion of Hg(II) into Hg(0) (Giri et al, 2014).…”