![]() The stabilization efficiencies of different metal-chelant complexes are not only related to their stability constant and availability but also associated with the solubility constants of metal sulfide. Additionally, less elevation degree of MC-washed alkaline soil pH after SRB treatment (~ 0.1) than those in the MC-washed acidic soil (0.72–1.02) was more conducive to adsorption of negatively charged metal-chelant complexes on the MC-washed alkaline soil. The inoculation of SRB into the MC-washed alkaline soil more successfully stimulated indigenous bacteria than the MC-washed acidic soil did, contributing to larger numbers of positive correlations between bacterial genera (dominantly from Firmicutes) and metal stabilization efficiencies in the MC-washed alkaline soil. SRB had higher stabilization efficiencies of metal-chelant complexes in the MC-washed alkaline soil (13.07–64.95%) than those in the MC-washed acidic soil (< 13%), mainly because alkaline condition was more favorable for the dechelation of metal-chelant complexes by SRB to form metal sulfide precipitation. The results showed that SRB treatment increased the reduction efficiencies of SO 4 2 - by 63.84–85.80% and 51.45–60.17% in the MC-washed alkaline and acidic soils, respectively. Bacterial community composition was analyzed by a high-throughput sequencing technique. Total and available heavy metals and soil physicochemical properties were measured. The treatment groups included CK-AL/AC (deionized water + soil), S-AL/AC ( Shewanella JN01 + soil), C-AL/AC ( Clostridium ZG01 + soil), and M-AL/AC (the mixed two strains + soil). The two SRB strains (10%, OD 600 = 1) and their mixture (v:v = 1:1) were inoculated into the mixed chelator (MC)–washed alkaline (AL) and acidic (AC) soils to treat the residual metal (Cd, Pb, Cu, and Zn)–chelant complexes. The study investigated the stabilization efficiencies of metal-chelant complexes by SRB in the chelator-washed soil and explored the relevant mechanisms. Sulfate-reducing bacteria (SRB) is considered a promising bioremediation technology for stabilization of metals in soil.
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