Study On Construction And Heavy-Metal-Capturing Capability Of Synthetic Bacterium-Magnetic Nanoparticle Co-Assemblies

Heavy metal pollution has become a worldwide problem severely threatening our health and ecosystem.The rapid development of genetic engineering and synthetic biology facilitates artificial modification and even de novo design of heavy-metal-capturing components,promoting the application of synthetic microorganisms in the field of heavy metal pollution treatment.Artificial organisms can effectively reduce the cost of heavy metal removal,greatly improving their efficiency of bioremediation.Magnetic nanoparticles（MNPs）are widely used in treating environmental pollution due to their superparamagnetic and magnetically separable properties.The study constructed co-assemblies of synthetic bacterial cells and magnetic nanoparticles based on synthetic biology and chemical engineering strategies.The formed biotic/abiotic co-assembling platform was able to efficiently capture heavy metals and be recycled by artificial magnetic fields,providing a new idea for application of synthetic microorganisms in treatment of heavy metal pollution.The main results are demonstrated as follows.（1）A de novo synthetic heavy-metal-capturing gene（syn HMB containing a six-histidine tag,two cystine-rich heavy-metal-capturing peptides,and a human metallothionein sequence）and a synthetic typeⅥsecretory system（T6SS）cluster of Pseudomonas putida were designed and synthesized by the synthetic biology strategy.The synthetic bacteria were successfully constructed by introducing the two synthetic modules into Escherichia coli.The synthetic bacteria displayed the heavy-metal-capturing protein Syn HMB on cell surface,exhibiting high heavy-metal-capturing and heavy-metal-tolerating capacity.（2）Magnetic nanoparticles were synthesized using a co-precipitation method,coated with a silica（Si O₂）shell under alkaline condition,and further covalently modified by polyethyleneimine（PEI）and the heavy-metal-chelating agent diethylenetriaminepentaacetic acid（DTPA）on the shell,obtaining the final magnetic nanoparticles MNP@Si O₂-PEI-DTPA with high heavy-metal-capturing capability.（3）Owing to surface exposure of the positively-charged histidine tag on the synthetic bacteria and the negatively-charged carboxyl groups on MNP@Si O₂-PEI-DTPA,the synthetic bacteria and the functionalized magnetic nanoparticles co-assembled through electrostatic interaction to form a biotic/abiotic complex,which exhibited a self-growing property.The co-assemblies captured heavy metals with high capturing efficiency(>90%even at 50 mg/L of Cd²⁺and 50 mg/L of Pb²⁺)from the culture medium,and were conveniently recycled by artificial magnetic fields.