Assessment of the bioremediation efficacy of the mercury resistant bacterium isolated from the mithi river

Abstract

The contamination of natural resources with mercury has gained attention due to its high toxicity to all life forms. Bioremediation of mercury using bacteria is a useful technique to remediate mercury contamination. In the present study mercury resistant bacteria (MRB) were isolated from Mithi River water samples. Total heterotrophic bacteria (THB) and MRB present in the Mithi river water samples were enumerated. The count for THB was found to be 3.7 × 106 CFU/ml. MRB enumerated in the nutrient agar medium with mercury concentrations of 50, 100 and 150 ppm had counts of 2.8 × 106, 9.1 × 105 and 5.8 × 104 CFU/ml, respectively. The minimum inhibitory concentration (MIC) of the isolated bacterium was found to be around 500 ppm of mercury, and it was selected for further analysis. The bacterial isolate was found to tolerate a wide range of salt concentrations from 5 to 35 ppt of NaCl. The bacterial isolate was characterized by using standard biochemical tests and identified by using the 16S rDNA technique. Homology analysis of the 16S rDNA gene has confirmed the identity of the bacterium as Bacillus thuringiensis strain RGN1.2 with NCBI accession no. KX832953.1. It could remove 96.72%, 90.67% and 90.10% of mercury in 48 hours at 10, 25 and 50 ppm of mercury.