Determination of Bacteria Resistance Threshold to Lead, Zinc and Cadmium in Three Kind of Industrial Waste water

Agricultural and specifically industrial activities have led to a substantial release of toxic heavy metals in the environment which can constitute a major hazard for ecosystem and human health. Biosorption of heavy metals is one of the most effective technologies involved in the removal of toxic metals from contamination sites that has used in the last decade. Population and microbial activity changes and decreases in water polluted with heavy metals. On the other hand, some of the microorganisms create the resistance mechanisms that make resistant species with metal tolerance ability. The lowest concentration of metal, which inhibits the growth of the microorganism, was considered as MIC. In this study, in order to determine the bacteria resistance threshold to Pb, Zn and Cd in three wastewater samples, they were cultured by spread plate method on PHG-?? agar includes of 0.5 mMl-1 of each metal, in three dilution and two replications, separately. After isolation the bacteria resistance to metals, Minimum Inhibitory Concentration of bacteria was specified with concentrations as 1, 2, 4 and 8 mMl-1. After enrichment, purification, bacterial slides preparation and gram staining, the kind of bacteria based on their morphology and gram reaction were specified. According to the acquired results, microbial activity and viable population size both decreased at the presence of heavy metals. In the studied samples, the average of MIC for Pb, were 2.57, 2.2 and 1.5 mMl-1, respectively and it was 2, 0 and 1.46 mMl-1 about Zn. All of the bacteria resistance to Cd showed MIC equal to 0.5 mMl-1. On the basis of obtained results, the most of resistance bacteria were gram positive. This study aimed to determine bacterial resistance threshold to metals to acquire a high efficiency in wastewater purification by bacteria.