Biosorption of Lead by Pseudomonas sp Isolated from Oil-Contaminated Wastewaters in Khuzestan

Biosorption is a most effective technology for the removal of such toxic substances as heavy metals. The objective of this study was four-fold: 1) to isolate lead resistant Pseudomonas strains, 2) to determine the optimal conditions of their growth, 3) to obtain the minimum inhibitory concentration of lead, and 4) to evaluate the bioremoval of lead from culture solutions. For the purposes of this study, oil-contaminated wastewater samples were collected from Khuzestan region and transferred to laboratory where they were homogenized and serially diluted up to 10-10 with sterile saline before they were cultured in Luria Bertani agar medium containing 5ppm of lead nitrate. Resistant strains were then isolated at 37°C for 24h. The samples were subsequently cultured in Macconkey agar for isolation of appropriate gram negative strains. Biochemical tests were used to identify the bacteria, 10 strains of which were screened as lead resistant ones from all the 24 isolates. The bacterial colonies were selected and tested with different concentrations (100- 2100 ppm) of lead for their resistance. The plates were then incubated at 37ºC for 24h and Mso1 was chosen from among the lead resistant colonies for further experiments. This strain showed resistance to chloramphenicol (30µg) and erythromycin (15µg) when subjected to the antimicrobial susceptibility test. Optimal growth conditions included a temperature of 40°C at 100 rpm and a pH level of 6 in the presence of lead by spectrophotometry at 600nm. Absorption tests showed that the Mso1 strain had a metal removal efficiency of 38.45% from an aqueous solution containing 100 ppm of lead over 24h. The results confirmed the capability of Pseudomonassp in the bioremediation of Pb-contaminated wastewaters.