Heavy metal resistance in Arthrobacter ramosus strain G2 isolated from mercuric salt-contaminated soil

Present study describes isolation of a multiple metal-resistant Arthrobacter ramosus strain from mercuric salt-contaminated soil. The isolate was found to resist and bioaccumulate several metals, such as cadmium, cobalt, zinc, chromium and mercury. Maximum tolerated concentrations for above metals were found to be 37, 525, 348, 1530 and 369 μM, respectively. The isolate could also reduce and detoxify redox-active metals like chromium and mercury, indicating that it has great potential in bioremediation of heavy metal-contaminated sites. Chromate reductase and mercuric reductase (MerA) activities in protein extract of the culture were found to be 2.3 and 0.17 units mg−1 protein, respectively. MerA enzyme was isolated from the culture by (NH4)2SO4 precipitation followed by dye affinity chromatography and its identity was confirmed by nano-LC-MS/MS. Its monomeric molecular weight, and optimum pH and temperature were 57 kDa, 7.4 and 55 °C, respectively. Thus, the enzyme was mildly thermophilic as compared to other MerA enzymes. Km and Vmax of the enzyme were 16.9 μM HgCl2 and 6.2 μmol min−1 mg−1 enzyme, respectively. The enzyme was found to be NADPH-specific. To our knowledge this is the first report on characterization of MerA enzyme from an Arthrobacter sp.