Fine Structure Analyses of Recombinant Escherichia coli with Heavy Metal Adsorption

• Main Authors: Yu-Ting Wang, 汪玉婷
• Other Authors: Kuen-Song Lin
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/80065310609203678975

碩士 === 元智大學 === 化學工程學系 === 92 === Gram-positive (Bacillus cereus RC607) and Gram-negative (Pseudomonas sp. K-62) merP genes encoding metal-binding proteins cloned and over-expressed in Escherichia coli BL21 hosts were studied in the present work. The MerP protein possessing a highly conserved with two cysteine residues (Cys-X-X-Cys) for heavy bonding was over-expressed via IPTG induction and the resulting recombinant strains were used to adsorb heavy metals in aqueous solutions of Pb2+, Cd2+, Hg2+, Ni2+, Zn2+, and Cu2+. Experimentally, the adsorption capacities of these metals for the merP or merP-free cells were carefully measured by using ICP-AES. The experimental results indicate that the metal adsorption capacity of merP or merP-free host cells for Pb2+, Cd2+, Hg2+, Ni2+, and Cu2+ all decreased in the order of G(B)>G(P)>BL21 whereas the trend was G(P)>G(B)>BL21 for Zn2+. The morphology or microstructures of cells markedly changed after metal adsorption and exhibited signals of merP host cell lysis by FE-SEM microphotos. The degree of transformation of the cells adsorbing metal cations analyzed by FE-SEM was Zn>Ni>Pb>Cd>Cu. The element analysis, oxidation states, fine structures of metals in merP or merP-free cells were also investigated by using XPS, EA, EDS, XANES or EXAFS spectroscopies. The XPS analysis shows that the of metal oxides excluding Pb species was higher than that of metal sulfides in higher metal adsorption capacity of in merP cells. From XANES data, valencies of all metal cations were 2. It showed that the metal cations might preferably attack SH groups and combined into M-S bonding. The EXAFS spectra indicating that the Cu-S, Ni-S, and Zn-S species in merP host cells had bond distances of 2.05, 2.16, and 1.97Å, respectively. Coordination numbers of the Cu, Ni, and Zn elements in merP host cells were 4, 6, and 6, respectively. These results might offer a further explanation of the transformation for more stable metal-S structures in cells postulated with plane or hexagonal bonding under complex environment.