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 fungi and bacteria 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 3200mg/L each of PbCl2, NiSO4 and CdCl2 while R. stolonifer was exposed to 3200mg/L of PbCl2, NiSO4 but 800mg of CdCl2. Furthermore, the two organisms were exposed to 1500mg/L of all the three metals (comprising 500mg/L of each heavy metal) for 96hours 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 (501.05mg) 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 bioaccumulation and consequently, their potential as bioremediation agents in polluted environments individually and in a synergistic growth.