ISOLATION, SCREENING AND IDENTIFICATION OF LEAD AND CADMIUM RESISTANT SULFUR OXIDIZING BACTERIA

Sulfur oxidizing bacteria (SOB) oxidize elemental sulfur (5 0 ) or reduce sulfur compounds to generate sulfuric acid which reduces the pH of media. In this study, lead and cadmium tolerant SOB were isolated by using thiosulphate medium from samples collected from different ecologies and screened on account of pH reduction, sulfate ions production, phosphorus solubilization index and phosphorus bioleaching tests. Results indicated that sulfate ions production (800 mg/L by Bacillus sp. strain SS-16) and phosphorus solubilization (713 mg/L by Bacillus sp. strain SS-16) from rock phosphate were significantly increased as compared to control due to pH reduction (net decrease of 4.52 points). The tolerance of isolated SOB by minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) was evaluated at different concentrations of lead and cadmium and Bacillus sp. strain SS-16 showed its ability to tolerate lead and cadmium up to 1000 and 180 mg/L, respectively. Organic acids production ability of three efficient isolated SOB (SS-4, SS-8 and Bacillus sp. SS-16) was evaluated under normal and stressed (lead and cadmium polluted) conditions. Results indicated that short chain organic acids amount increased under Pb and Cd stressed conditions as compared to normal medium. The isolated SOB were further studied for their morphological and biochemical properties. The most efficient bacterium belonged to sewage sludge ecology and was identified as Bacillus sp. SS-16.