Biological reduction of heavy metal pollutant, hexavalent chromium (Cr (VI)), by Gram-negative bacterium Escherichia coli ATCC 33456 was investigated in a batch growth system. Concentration of Cr(VI) selected for the growth experiment was varied between 0, 5, 10, 20, 30, 40, and 50 ppm and pH of each medium was not controlled in order to monitor the trends. Results showed that during growth on the EC medium supplemented with 5 or 10 ppm of Cr(VI), E. coli was able to remove the cation to as lower concentration as 0.01 ppm and the cells grew at average specific growth rate of 0.1 per hour. Above Cr(VI) concentration of 10 ppm, cell cultures were still able to reduce the cation with removal efficiency of about 70% but without any growing cells. However, in the medium supplemented with up to 50 ppm of Cr(VI) removal capability of the cells decreased sharply and no growth was detected. In the medium amended with lower Cr (VI) concentration, cation removal occurred during the lag growth phase, which might explain that the intra-cellular surface interaction was the major mechanism. When Cr(VI) concentration was higher than 20 ppm, the removal also occurred but only during the exponential growth phase, indicating the involvement of the intra-cellular detoxification mechanism.
Author: Yalun Arifin, Mangihot Tua Gultom, Elisabeth Davina Prayitno, dan Adi Wibowo Soepardiman