Iranian Journal of Medical Microbiology

Background and Objectives: Mercury is one of the most toxic heavy metals as it cause chronic and acute toxicity, visually, hearing and neurological systems Impaired in low concentrations. Mercury polluted sites bacteria can remove this metal from their surrounding by reduction process. Domestic, commercial, industrial, hospital and agricultural effluents of Shiraz city enter to the Lake Maharloo through Khoshk, Pole Fasa and Salamiye rivers and contaminate it. Heavy metals especially mercury are among this river pollutants. Purpose of this study was isolation and identification of mercury resistant halophilic bacteria from water and sediments of Lake Maharloo and survey their growth kinetics.

Materials and Methods: Sampling were done from surface water and sediments of 4 stations of the lake (entrance of Khoshk, Pole Fasa and Salamiye rivers and middle of lake) in 4 season during years 2009-2010. Mercury resistant halophilic bacteria were isolated by enriching in Luria Bertani Broth and Luria Bertani Agar media containing salt and mercury and counted by Viable Plate Count method. Afterwards their growths kinetics were surveyed in three states: without mercury (control), presence of 5 mg/l mercury from the first and presence of 5 mg/l mercury from the half of logarithmic growth phase. ANOVA and Duncan tests were used for statistical analysis.

Results: The most numbers of mercury resistant bacteria were obtained by 2.8 × 10⁴ and 8.375 × 10³   (based on CFU/ml or CFU/g) from Khoshk and Pole Fasa stations respectively and the lowest numbers was from the middle of lake (7×10²). Vibrio, Citrobacter, Staphylococcus, Proteus, E. Coli and Pseudomonas were identified as mercury resistant bacteria.  The most and least abundance percentage of identified bacteria from different stations and seasons were related to Vibrio with 75% and Citrobacter with 12.5% respectively. Growth of Citrobacter and Staphylococcus declined sharply in presence of mercury from their half of logarithmic growth phase.

Conclusion: Mercury resistant bacteria have determinant role in absorption and elimination of this metal from Lake Maharloo. With preparation of appropriate condition and bed for growth of these bacteria, they can be used for detoxification and mercury removal from effluents of Lake Maharloo environmental pollutant plants.