Cysteine-induced sulfide bioprecipitation enables simultaneous efficient dechlorination and cadmium removal by Pseudomonas sp. CP-1

Organohalides and heavy metals often co-contaminate groundwater, however, the biotoxicity of heavy metal strongly inhibits microbial reductive dechlorination activity and existing bioremediation strategies seldom achieve simultaneous removal of both types of pollutants. Here, we demonstrated that cysteine amendment enabled synchronous reductive dechlorination and cadmium (Cd(II)) removal in an organohalide-respiring bacterium Pseudomonas sp. CP-1 through cysteine-mediated sulfide bioprecipitation. Batch experiments revealed that cysteine supplementation at a Cd(II):Cys molar ratio of 1:2 achieved an enhanced 2,4,6-trichlorophenol dechlorination kinetics (k_d = 0.28 D^-1) and 91.20% recovery of Cd(II) as nanocrystalline CdS deposited on the cell surface. In simulated continuous-flow biobarriers, the addition of cysteine sustained high removal efficiencies for both contaminants despite hydraulic fluctuations, with a highest dechlorination rate reaching 120 µM·(L·d)^-1, 9.6 times higher than the pure dechlorination process. Multi-omics analysis revealed the potential coupled metabolic mechanism of dechlorination and Cd(II) removal in which the amendment of cysteine not only activated cysteine desulfurase to produce H₂S for extracellular precipitation of CdS, but also generated alanine and pyruvate, which likely assimilated into the TCA cycle to augment NADH production and electron supply for reductive dechlorination. This work establishes a unique single-strain based strategy for synergistic remediation of organohalide and heavy metal ions in groundwater, highlighting the potential of cysteine-driven metabolism as an effective bioaugmentation tool for sustainable remediation of organohalide and heavy metal co-contaminated groundwater.