Selective Isolation of Heavy metals Resistant Bacteria From Waste Water

Abstract

The current study was conducted to isolate bacteria resistant to heavy metals lead, chromium and cadmium from waste water. The concentration of lead, chromium and cadmium was measured in the waste water samples collected from different sites in Baghdad city using a flame atomic spectrometry. The results showed a significant increase in metals concentration in some sites compared to the standard determinants, as well as a significant variation between the concentration of the three metals, and nil values were recorded in some sites.
The primary isolation of lead, chromium and cadmium tolerant bacteria from five sites which recorded the highest concentration of these metals showed 25 bacterial isolates distributed between 9 bacterial isolates tolerating 300 mg/l lead, 9 isolates tolerant to 100 mg/l chromium and 7 isolates tolerant to 100 mg/l of cadmium. Well diffusion method was used to choose resistant bacterial isolates, and the results showed a difference in the resistance of bacterial isolates to metals, and the bacterial isolates Pb1, Pb4, Cr8, Cr9, Cd5 were chosen which recorded resistance to high concentrations of heavy metals and more than one metal at the same time. The maximum tolerance concentration of the bacterial isolates was determined using liquid medium, and the bacterial isolate Pb1 recorded a maximum tolerance concentration of 1300, 700, 350 mg/l for lead, chromium and cadmium respectively, while the isolate Pb4 recorded the maximum tolerance concentration of 2300 mg/l for lead, and 700 mg/l for chromium, 300 mg/l for cadmium. The isolate Cr8 showed a maximum tolerance concentration of 700, 650, and 450 mg/l for lead, chromium and cadmium respectively, while the bacterial isolate Cr9 showed a maximum tolerance concentration of 700 mg/l for both lead and chromium and 500 mg/l for cadmium, while the bacterial isolate Cd5 recorded the highest maximum cadmium tolerance 650 mg/l among bacterial isolates, with a maximum tolerance concentration 800 mg/l for lead and 550 mg/l for chromium. Primary identification showed that all five bacterial isolates were Gram negative bacteria.