Microbiology Research Journal International

Aim: We studied the potentials of four metal-resistant bacterial strains to reduce the concentration of selected metals in dumpsite leachate.

Methods: The bacteria which were obtained from the culture collection of the Environmental Microbiology and Biotechnology laboratory were subjected to increasing concentration of metals in a metal-supplemented medium. The bacteria were then introduced into a batch culture biosorption set-up containing the culture medium and tyndallized leachate and the residual metal concentration was determined after a 14-day incubation period using the atomic absorption spectrophotometer (AAS), after the bacterial cells had been separated from the leachate by centrifugation at 10000 rpm for 15 min.

Results: 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. The biosorption set up showed that Paenalcaligenes hominis had a higher percentage reduction for Pb in the leachate with a reduction of 35.77%, while Bordetella petrii removed the highest concentration of Cd and Ni in the leachate with values of 32.81% and 34.91% respectively. However the highest percentage reduction for Cr (32.54%) was observed when the leachate was treated with a consortium of the four bacterial strains.

Conclusion: This study revealed that these metal-resistant bacteria could be very useful in the biological treatment of metal-containing wastewater.