Screening and molecular identification of Mercury Tolerant Bacteria from Dairy Waste and Evaluation of their Bioremediation Potential by Atomic Absorption Spectroscopy

The present study aimed to isolate, to screen and to identify molecularly mercury-resistant bacteria from industrial effluents and to evaluate their mercury-reducing potential using Atomic Absorption Spectroscopy (AAS). Effluent samples from the dairy industries in Pune city were collected and enriched in nutrient broth supplemented with HgCl₂ for the isolation of mercury-resistant bacterial isolates. The isolates were obtained on different agar media (Nutrient Agar, LB Agar, Minimal Agar and Mueller–Hinton Agar) containing mercury concentrations ranging from 10 ppm to 200 ppm. The morphological and biochemical characterizations were performed for selected isolates. The mercury reduction by selected isolates was evaluated by using AAS over 48 hours. Molecular identification of potent isolates was performed by 16S rRNA gene sequencing, followed by phylogenetic analysis using MEGA 11 software. Out of 25 isolates, three isolates H1, H6, H7 exhibited growth at 200 ppm HgCl₂, while K1 exhibited growth at 100 ppm concentration of HgCl₂. Based on AAS analysis, H1 and H6 demonstrated the highest mercury reduction, 7.44 ppm and 16.76 ppm respectively after 30 hours of incubation. Morphological, biochemical and molecular characterization revealed H1 as Pseudomonas aeruginosa and H6 as Bacillus paranthracis. The study demonstrated that Pseudomonas aeruginosa and Bacillus paranthracis isolates possess strong mercury reduction capabilities, highlighting their potential applications in the bioremediation of mercury-contaminated environments.