Heavy Metal Resistance in Bacteria Isolated from Contaminated and Uncontaminated Soils

Abstract

The general tolerance levels of heterotrophic bacterial populations to one or more metals can be determined by assessing their resistance to such metals. Soil bacterial communities from one uncontaminated and one metal impacted soil were analyzed to determine their resistance to some heavy metals by plating media amended with different concentrations of the metal ions. It was found that the metal-contaminated soil communities were more resistant than the uncontaminated community. In addition, the highest minimum inhibitory concentration (MIC) of more than 1000 μg/ml was observed against Pb2+ in 25% and 15% of the isolates in the contaminated and uncontaminated soils, respectively. On the other hand, the MIC for Cu2+ and Cr6+ ranged between 200 and 600 μg/ml. Most bacterial isolates from the soil were resistant to very high concentrations of heavy metals regardless of the level of metal concentrations in their environment. It is proposed that the resistance ability of the isolates could be exploited in considering the isolates as possible candidates for the decontamination of metal-polluted sites. The most predominant isolates at high concentrations of the metal ions include Bacillus spp., Pseudomonas spp., Corynebacterium spp., Micrococcus spp. and Flavobacterium spp.