Study of Copper Resistant Pseudomonas Strains Isolated from Soil in Sarcheshmeh Copper Mine, in Iran and Investigation of the Mechanisms Involved in Copper Resistance

Heavy metal contaminated sites are the potential source of metal resistance microorganisms. The major focus of this study is to isolate and identify copper ions resistant Pseudomonas from the soil samples collected from mining and refining sites of Sarcheshmeh copper mine in the Kerman Province of Iran and investigate on possible mechanisms for copper resistance. Isolates were selected based on high level of copper ions resistance. The screened isolate was identified as Pseudomonas putida Cu-2 by morphological, biochemical and 16S rDNA gene sequencing analysis. A high degree of copper ions resistance associated with multiple antibiotic resistances was also detected in the screened isolate. The growth pattern of screened isolate with all the studied Cu concentrations was similar to that of control (without Cu ions) indicating that Cu ions would not affect the growth of isolated strain. A decrease in the amount of exopolysaccharides (EPS) was detected after Cu ions - P. Putida Cu-2 culture supernatant interaction. The Fourier transform infrared spectroscopy (FT-IR) peaks for the EPS extracted from the bacterial culture supernatant and the interacted Cu ions were nearly similar. The EPS covering of the Cu ions was established by FT-IR. The study of bacterial EPS covered Cu ions with E. coli PTCC 1338 and S. aureus PTCC 1113 exhibited less toxicity compared to uncoated Cu ions. The presence of copA gene that encodes for the multi-copper oxidase was investigated in the selected strain. The present study suggests that the capping of Cu ions by bacterially produced EPS and the presence of copA gene serve as the probable mechanisms of copper resistance.