Reduction of heavy metal concentration in liquids by Rhizobium polysaccharides
1990
Mamaril, J.C. | Paner, E.T. | Capuno, V.T. | Trinidad, L.C. (Philippines Univ., Los Banos, College, Laguna (Philippines). National Inst. of Biotechnology and Applied Microbiology)
Five strains of Rhizobium sp. isolated from the roots of Leucaena leucocephala (ipil-ipil) and one from Glycine max (soybean) were observed to synthesize predigious amounts of extra cellular mucilaginous polysaccharides. These strains were tested to find out how effective they were in reducing the concentrations of heavy toxic metals, Hg, Cd and Pb from liquid media. The use of rhizobial polysaccharides as sequestering agents for heavy metals will provide a new technology for environmental management. The rhizobial strains were grown in yeast extract monnitol broth (YEMB) containing the heavy metal at two concentrations, 500 microgram and 1000 microgram/L. These concentrations are 10 to 100 times higher than the WHO limits for these toxic metals. Concentrations of 10, 20, and 30 ppm of the metals were also studied. The period of incubation ranged from 4 to 10 days; after which the cell culture was centrifuged and the supernatant analyzed for its heavy metal content by isotachophoretic methods of analysis. Results show a drastic reduction of heavy metal concentration in the supernatant to below WHO limits of 10 microgram/L Cd and 100 micrograpm/L Pb. Transmission electron micrographs of Rhizobium sp. grown in YEMB with heavy metals showed dense extracellular areas.
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