P47: 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∼99.9% of the Cd(II), whereas the control strain removed only 11.4∼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. The morphology of the biofilms formed by Caulobacter crescentus recombinant strain JS4022/p723-6H, which expresses hexahistidine peptides anchored to its surface layer protein RsaA, was examined.  The density of the biofilm reached a maximum after 48 h of incubation and was not affected by exposure to cadmium. When treated with 0.4 ppm Cd(II), biofilms formed by the engineered strain removed 76.9% of the total metal, whereas a control strain only retained 13.5%. This work provides a potential cost-effective solution toward bioremediation of heavy metals from aqueous systems, and to construct large scale remedial bioreactors in a cost effective manner.