Bacteria metabolically engineered for enhanced phytochelatin production and cadmium accumulation.

Phytochelatins (PCs) with good binding affinities for a wide range of heavy metals were exploited to develop microbial sorbents for cadmium removal. PC synthase from Schizosaccharomyces pombe (SpPCS) was overexpressed in Escherichia coli, resulting in PC synthesis and 7.5-times-higher Cd accumulation. The coexpression of a variant gamma-glutamylcysteine synthetase desensitized to feedback inhibition (GshI) increased the supply of the PC precursor glutathione, resulting in further increases of 10- and 2-fold in PC production and Cd accumulation, respectively. A Cd transporter, MntA, was expressed with SpPCS and GshI to improve Cd uptake, resulting in a further 1.5-fold increase in Cd accumulation. The level of Cd accumulation in this recombinant E. coli strain (31.6 micromol/g [dry weight] of cells) was more than 25-fold higher than that in the control strain.