| Abstract: |
Tolerance of 80 bacterial cultures isolated from wastewater of four factories to different heavy metals concentrations were studied in the laboratory. The most six tolerant-bacterial isolates to the different concentrations of heavy metals were chosen for further studies. These six isolates were identified as Brevundimonas vesicularis (C18), Klebsiella mobilis (C19), Bacillus circulans (D21), Salmonella choleraesuis (F15), E. coli (P4) and E. coli (P7). The effects of some environmental factors such as pH, temperature, and incubation periods on the biosorption of three heavy metals namely Cd, Pb and Zn were tested. The maximum biosorption of Cd, Pb and Zn by Brevundimonas vesicularis (C18) was obtained at pH 5; however, there was no significant difference between pH values at 5 and 6 of the biosorption of Cd or Zn. The optimum temperature for biosorption of either Cd or Pb was obtained at temperature ranged between 25-35oC. The suitable incubation periods for biosorption of Cd, Pb and Zn were 48, 36 and 24 h, respectively. Structural and morphological changes in Brevundimonas vesicularis and Bacillus circulans cells grown on T-medium containing sublethal concentration of heavy metals for 48 h have been examined by transmission electron microscopy (TEM). Irregular shapes were observed in these strains after exposure to Cd ions as a wrinkling in the cell wall. Some visible electron dense particles were observed within these cells after treated with Zn ions (100 mg/L). The RAPD fingerprints showed substantial differences between unexposed and exposed bacterial cells to Cd, Pb and Zn, with apparent changes in the numbers and sizes of the amplified DNA fragments of Brevundimonas vesicularis (C18) and Bacillus circulans (D21). An applied experiment was conducted in an insect proof house at the Faculty of Agriculture, Zagazig University to investigate the capability of some heavy metals-resistance bacteria [Brevundimonas vesicularis (C18), Klebsiella mobilis (C19) and Bacillus circulans (D21)] to protect lettuce plants grown on polluted sand cultures at different concentrations of cadmium, lead and zinc. The results showed that application of bacterial cells together with heavy metals resulted in increases in the fresh and dry weights of lettuce plants compared with the treatments when metals were applied without bacteria. Also, these bacterial strains were used for bioremoval of heavy metals from wastewater of two factories (food and dye). The results showed that addition of bacterial cells to the wastewater resulted in removal a lot of heavy metals from the wastewater with various percentages.
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