Genetic Engineering of Caulobacter crescentus for Removal of Cadmium from Water

Hexa-histidine (6His) peptide was inserted to a permissive site of the surface layer (S-layer) protein RsaA of Caulobacter crescentus. The recombinant strain JS4022/p723-6H, expressing RsaA-6His fusion protein was examined for its ability to sequester Cd (II) from the bacterial growth medium. When mixed with 1 ppm CdCl2, JS4022/p723-6H removed 94.3 similar to 99.9% of the Cd(II), whereas the control strain removed only 11.4 similar to 37.0%, depending on experimental conditions. The effective contact time of the cells and Cd(II) was as short as 15 min. When higher concentrations of CdCl2 were tested, JS4022/p723-6H consistently demonstrated enhanced binding capacity over the control strain. At 15 ppm of Cd(II), each gram of JS4022/p723-6H dry cells retrieved 16.0 mg of Cd(II), comparing to 11.6 mg g(-1) achieved by the control strain. This work provides a potential cost-effective solution toward bioremediation of heavy metals from aqueous systems.