title: Enhanced bioaccumulation of heavy metals by bacterial cells displaying synthetic phytochelatins.
abstract: A novel strategy using synthetic phytochelatins is described for the purpose of developing microbial agents for enhanced bioaccumulation of toxic metals. Synthetic genes encoding for several metal-chelating phytochelatin analogs (Glu-Cys)(n)Gly (EC8 (n = 8), EC11 (n = 11), and EC20 (n = 20)) were synthesized, linked to a lpp-ompA fusion gene, and displayed on the surface of E. coli. For comparison, EC20 was also expressed periplasmically as a fusion with the maltose-binding protein (MBP-EC20). Purified MBP-EC20 was shown to accumulate more Cd(2+) per peptide than typical mammalian metallothioneins with a stoichiometry of 10 Cd(2+)/peptide. Cells displaying synthetic phytochelatins exhibited chain-length dependent increase in metal accumulation. For example, 18 nmoles of Cd(2+)/mg dry cells were accumulated by cells displaying EC8, whereas cells exhibiting EC20 accumulated a maximum of 60 nmoles of Cd(2+)/mg dry cells. Moreover, cells with surface-expressed EC20 accumulated twice the amount of Cd(2+) as cells expressing EC20 periplasmically. The ability to genetically engineer ECs with precisely defined chain length could provide an attractive strategy for developing high-affinity bioadsorbents suitable for heavy metal removal.
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside CA 92521, USA.
authors.forename: W
authors.initials: W
authors.lastname: Bae
authors.forename: W
authors.initials: W
authors.lastname: Chen
authors.forename: A
authors.initials: A
authors.lastname: Mulchandani
authors.forename: R K
authors.initials: RK
authors.lastname: Mehra
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D002104:Cadmium / Q000378:metabolism; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005818:Genetic Engineering / Q000379:methods*; D005978:Glutathione; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism; D008667:Metalloproteins / Q000235:genetics* / Q000378:metabolism; D019216:Metals, Heavy / Q000378:metabolism*; D008969:Molecular Sequence Data; D054811:Phytochelatins; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D008074:Lipoproteins; D008667:Metalloproteins; D019216:Metals, Heavy; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D002104:Cadmium; C078167:OMPA outer membrane proteins; D054811:Phytochelatins; D005978:Glutathione