Bioremediation of heavy metal ion (Cu2+) by live probiotic Janus microparticles using droplet-based microfluidic technique

Heavy metals bring a serious threat to human life because of their toxicity and non-biodegradability. Bioremediation is an effective and green strategy for the removal of hazardous substances by natural biological processes. However, the application of microorganisms has been largely limited because planktonic microorganisms have difficulty resisting harsh environments and are challenging to recover in nature. Herein, living probiotic Janus microparticles with magnetic property were prepared using droplet microfluidic and photo-crosslinking technology. Saccharomyces boulardii (S. boulardii), a probiotic fungus currently used in clinical treatment, was encapsulated in a hemisphere of Janus microparticles. The survival rates of S. boulardii encapsulated in the polyethylene glycol diacrylate hemisphere on day 10 and day 15 were above 90 %, and no S. boulardii was released from hydrogel hemisphere. Such living probiotic Janus microparticles could effectively remove copper ions (Cu²⁺) from wastewater, with the removal rate of Cu²⁺ reaching 64.78 % after 7 d. The adsorption capacity of S. boulardii in microparticles reached 51.83 mg/g. The cell viability of encapsulated S. boulardii was five times higher than that of free S. boulardii after exposed to Cu²⁺ for 5 d. Energy spectrum analysis showed that copper was accumulated in cytoplasm of S. boulardii. RNA-sequencing and western blotting results demonstrated the removal of Cu²⁺ by S. boulardii Janus microparticles mainly rely on copper/zinc superoxide dismutase-mediated biotransformation process. This work provides a green and sustainable strategy for the bioremediation of wastewater.