Biochemical Characterization of High Mercury Tolerance in a Pseudomonas Spp. Isolated from Industrial Effluent

A mercury resistant Pseudomonas spp. was isolated from industrial effluent that was able to tolerate 200 µM HgCl2. The Hg2+-resistant Pseudomonas spp. exhibited elevated stress-regulatory mechanisms as indicated by its high and inducible mercury reductase activity, high intrinsic catalase activity and enhanced resistance to Hg2+-induced release of protein-bound iron. An enhanced resistance of the bacterium to Hg2+-induced lipid peroxidation was observed as indicated by 40% lower conjugated diene and 60% lower lipid hydroperoxide content compared to a non-mercury resistant strain Pseudomonas aeruginosa (ATCC 27853). Phospholipid (PL) analysis of both the species reveled intrinsic differences in their PL composition. We observed 80% PE, 15% PG and 5% of an unidentified PL (U) in MRP compared to 65% PE, 20% PG and 17% CL in Pseudomonas aeruginosa (ATCC 27853). Mercury toxicity led to significant reorganization of PL in Pseudomonas aeruginosa (ATCC 27853) compared to MRP. While HgCl2 led to 25% increase in PE, 35% depletion in CL and 27% depletion in PG content of Pseudomonas aeruginosa (ATCC 27853), MRP exhibited only 5% enhancement in PE content that was accompanied by 20% depletion in PG content, indicating that MRP resists mercury induced PL organization. Interaction of the MRP with polystyrene surface showed two fold higher Hg2+-induced exopolysaccharide secretion and elevated biofilm forming ability compared to Pseudomonas aeruginosa (ATCC 27853). Our investigation reveals a novel Pseudomonas spp. with high Hg2+-tolerance mechanisms that can be utilized for efficient bioremediation of mercury