Utilization of metal-resistant bacteria in the detoxification of contaminated dumpsites

Abstract

The potentials of four metal-resistant bacterial strains to reduce the concentration of selected metals in dumpsite leachate were studied. The Environmental Microbiology and Biotechnology laboratory's culture collection of bacteria was used to extract the bacteria, which were then exposed to progressively higher metal concentrations in a medium enriched with metals. After the bacterial cells had been separated from the leachate by centrifugation at 10000 rpm for 15 min, the bacteria were then added to a batch culture biosorption set-up containing the culture medium and tyndallized leachate. The residual metal concentration was then determined after a 14-day incubation period using the atomic absorption spectrophotometer (AAS). The bacterial strains demonstrated high resistance to the four selected heavy metals [lead (Pb), chromium (Cr), cadmium (Cd) and nickel (Ni)] and their combination. The Minimum Inhibitory Concentration (MIC) value for the strains on the metal-incorporated medium for all the selected metals ranged from 700-1500 µg/ml. The resistance to the metals was in the order: Pb ˃ Ni ˃ Cr ˃ Cd. Pseudomonas aeruginosa had the highest MIC to the metal combination (1300 µg/ml) while the lowest was Proteus mirabilis (800 µg/ml); Paenalcaligenes faecalis and Bordetella petrii had MIC values of 1000 µg/ml and 1200 µg/ml respectively. Bordetella petrii removed the highest concentration of Cd and Ni from the leachate, with values of 32.81 percent and 34.91 percent, respectively, according to the biosorption setup, while Paenalcaligenes hominis had a higher percentage reduction for Pb in the leachate with a reduction of 35.77 percent. However, when the leachate was treated with a combination of the four bacterial strains, the largest percentage decrease for Cr (32.54 percent) was seen. According to this research, these metal-resistant bacteria might be highly helpful in the biological treatment of wastewater that contains metals.