Mercury (II) removal by resistant bacterial isolates and mercuric (II) reductase activity in a new strain of Pseudomonas sp. B50A

• Eight Gram-negatives bacterial isolates were resistant to high concentrations of mercury.
• The isolated Pseudomonas sp. B50A removed 86% of the mercury present in the medium.
• In the crude extract of this strain was detected mercuric (II) reductase activity.
• The isolate and the enzyme detected were effective in reducing Hg(II) to Hg(0).
• The results suggest that this microorganism has potential to bioremediation technologies.

This study aimed to isolate mercury resistant bacteria, determine the minimum inhibitory concentration for Hg, estimate mercury removal by selected isolates, explore the mer genes, and detect and characterize the activity of the enzyme mercuric (II) reductase produced by a new strain of Pseudomonas sp. B50A. The Hg removal capacity of the isolates was determined by incubating the isolates in Luria Bertani broth and the remaining mercury quantified by atomic absorption spectrophotometry. A PCR reaction was carried out to detect the merA gene and the mercury (II) reductase activity was determined in a spectrophotometer at 340 nm. Eight Gram-negative bacterial isolates were resistant to high mercury concentrations and capable of removing mercury, and of these, five were positive for the gene merA. The isolate Pseudomonas sp. B50A removed 86% of the mercury present in the culture medium and was chosen for further analysis of its enzyme activity. Mercuric (II) reductase activity was detected in the crude extract of this strain. This enzyme showed optimal activity at pH 8 and at temperatures between 37°C and 45°C. The ions NH4+, Ba2+, Sn2+, Ni2+ and Cd2+ neither inhibited nor stimulated the enzyme activity but it decreased in the presence of the ions Ca2+, Cu+ and K+. The isolate and the enzyme detected were effective in reducing Hg(II) to Hg(0), showing the potential to develop bioremediation technologies and processes to clean-up the environment and waste contaminated with mercury.