Microbial Remediation of Heavy Metals Contaminated Media by Bacillus megaterium and Rhizopus stolonifer

Abstract

There have been several researches on the bioremediation of heavy metals using microorganisms. However there is paucity of information on the use of synergistic heavy metal tolerant bacteria and fungi for the bioremediation of heavy metals. Bacillus megaterium and Rhizopus stolonifer isolated already and identified to tolerate lead, cadmium and nickel contamination were selectively investigated for heavy metal bioremediation. B. megaterium was exposed to 3200 mg/L each of PbCl2, NiSO4 and CdCl2 while R. stolonifer was exposed to 3200 mg/L of PbCl2, NiSO4 but 800 mg of CdCl2. Furthermore, the two organisms were exposed to 1500 mg/L of all the three metals (comprising 500 mg/L of each heavy metal) for 96 hrs at 30 °C. At the end of the study, the synergistic growth of R. stolonifer and B. megaterium had the maximum uptake of Pb (541.50 mg). Also the individual growth of B. megaterium and R. stolonifer had the highest uptake of Ni (501.05 mg) and Cd (479.10 mg) respectively. The highest uptake of the combined heavy metals was by B. megaterium. For individual metal contaminations, the synergistic growth of the microbes led the highest loss of Pb (25.24%) and the lowest loss of Ni (40.41%). In the case of the combined metal contamination, the synergistic growth of the microbes suppressed the bioremediation efficacy of B. megaterium and improved the efficacy of R. stolonifer. There was slight negative correlation between the pH and the percentage loss of the heavy metals from the medium (p = 0.885) and between the optical density and percentage heavy metal loss (p = 0.901). The results showed the effectiveness of these organisms for heavy metal bioremediation and consequently, their potential as bioremediation agents in polluted environments individually and in a synergistic growth and that such occurs through bioaccumulation.