A new plant–microbe strategy could change how wastewater heavy-metal pollutants are managed: instead of merely capturing toxic cadmium and lead, it converts them into light-harvesting semiconductor nanoparticles on living bacteria. The system pairs water lettuce with an engineered, fast-growing aerobic bacterium that colonizes roots, uses plant exudates as fuel, and performs sulfate reduction in the oxygen-rich rhizosphere. This produces hydrogen sulfide that precipitates metals as cadmium sulfide and lead sulfide particles anchored to bacterial cells. The resulting semiconductor–cell biohybrids show photoelectric activity, while bacterial auxin helps offset metal stress in the plant. The work links remediation with material recovery and offers a route to recover value from pollutants rather than landfilling contaminated plant biomass.
Conventional physical and chemical treatments can remove over 90% of heavy metals, but they often require energy-intensive steps and can generate secondary pollution. Phytoremediation is greener, yet plants mainly store metals in biomass, creating hazardous waste rather than recoverable products. Microbial biomineralization can make valuable metal sulfide nanomaterials, but many high-performing sulfide-producing microbes are sulfate-reducing bacteria that grow slowly and are inhibited by oxygen, including oxygen released from plant roots. Common rhizobacteria can alleviate metal stress, but they usually need external cysteine or other sulfur supplements to form metal sulfides. Given these challenges, in-depth research is needed on oxygen-tolerant, root-colonizing microbial systems that can couple wastewater treatment with heavy-metal upcycling.
Researchers from Harbin Institute of Technology (Shenzhen), Shenzhen Polytechnic University, Zhejiang Shuren University and the Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, report (DOI: 10.1016/j.ese.2026.100780). the system in Environmental Science and Ecotechnology . The article was accepted on 21 October 2026 and is available as a Journal Pre-proof (final Version of Record not yet assigned). The team engineered Vibrio natriegens to colonize water lettuce (Pistia stratiotes) roots and assemble cadmium sulfide (CdS) and lead sulfide (PbS) nanoparticles in the rhizosphere under aerobic conditions, then characterized metal removal, plant physiology and biohybrid photoelectric properties.
The engineered strain, XG203, carries cdsH, which encodes cysteine desulfhydrase, and a mutant cysE, which encodes serine acetyltransferase. It uses root exudates—mainly fatty acids, phosphates, alcohols, carbohydrates, amines and organic acids—to support growth. After inoculation, the bacteria colonized root crowns and root hairs within 24 hours. In aerobic culture, the strain reduced sulfate and generated hydrogen sulfide (H₂S), precipitating Cd²⁺ and Pb²⁺ as cell-surface-anchored CdS and PbS nanoparticles. Isolated CdS particles averaged about 4.94 nanometers (nm), showed cubic crystallinity, a direct bandgap of about 2.44 electron volts (eV) and photocurrent response. Over two treatment cycles, the plant–bacteria system maintained average per-cycle removal efficiencies of 30.12% for Cd and 63.50% for Pb from the aqueous phase, outperforming plants alone; free-living bacteria removed less than 3.03%. The bacteria also secreted indole-3-acetic acid (IAA), increasing root dry weight by 11.50% under Cd stress and 10.04% under Pb stress relative to uninoculated stressed plants. Photosystem I (PSI) metrics improved with inoculation, indicating reduced metal-induced photosynthetic impairment. The authors estimate that about 9.89% of Cd and 8.93% of Pb were associated with bacterial biohybrids, with the rest distributed among plant tissues and matrix-associated fractions.
The authors said the advance lies in moving sulfide biomineralization from oxygen-sensitive anaerobic niches into the oxygen-rich rhizosphere. They said the engineered bacterium uses root exudates to support growth without an external carbon source in the plant–bacteria system, couples aerobic sulfate reduction to metal capture, and turns a treatment liability into a photoelectrically active material. They said the system also supports the host plant by supplying IAA, helping roots recover biomass under metal stress. They said the next step is to test stability, microbial competition and biocontainment under field-relevant conditions.
The approach points to decentralized wastewater treatment and resource recovery, especially in constructed wetlands, agricultural runoff systems and other sites where long-term environmental compatibility matters. Recovered semiconductor–cell biohybrids could be used for solar-driven biosynthesis, photocatalysis or photoelectrochemical sensing, although they are recovered as root-associated materials rather than purified nanoparticles. Because metal sulfides have lower leaching potential than conventional hydroxide precipitates, the strategy may suit long-term restoration. The authors caution that performance will depend on sunlight, hydraulic residence time, ion interference and microbial competition. Field trials, long-term stability tests, biocontainment strategies and regulatory assessment are needed before responsible scale-up in real wastewater systems.
