A novel strategy using synthetic phytochelatins is described for the purpos
e of developing microbial agents for enhanced bioaccumulation of toxic meta
ls. Synthetic genes encoding for several metal-chelating phytochelatin anal
ogs (Glu-Cys)(n)Gly (EC8 (n = 8), EC11 (n = 11), and EC20 (n = 20)) were sy
nthesized, linked to a Ipp-ompA fusion gene, and displayed on the surface o
f E. coli. For comparison, EC20 was also expressed periplasmically as a fus
ion with the maltose-binding protein (MBP-EC20). Purified MBP-EC20 was show
n to accumulate more Cd2+ per peptide than typical mammalian metallothionei
ns with a stoichiometry of 10 Cd2+/peptide. Cells displaying synthetic phyt
ochelatins exhibited chain-length dependent increase in metal accumulation.
For example, 18 nmoles of Cd2+/mg dry cells were accumulated by cells disp
laying EC8, whereas cells exhibiting EC20 accumulated a maximum of 60 nmole
s of Cd2+/mg dry cells. Moreover, cells with surface-expressed EC20 accumul
ated twice the amount of Cd2+ as cells expressing EC20 periplasmically. The
ability to genetically engineer ECs with precisely defined chain length co
uld provide an attractive strategy for developing high-affinity bioadsorben
ts suitable for heavy metal removal. (C) 2000 John Wiley & Sons, Inc. Biote
chnol Bioeng 70: 518-524, 2000.