Phosphate-solubilizing bacteria enhance cadmium phytoremediation by Solanum nigrum L. through improved phosphorus...

Phosphate-solubilizing bacteria (PSB)-assisted phytoremediation has been recognized as an effective strategy for remediating cadmium (Cd)-contaminated soils, yet species-specific physiological and ecological traits among hyperaccumulators result in distinct Cd uptake mechanisms. Although the pivotal role of phosphorus (P) cycling in promoting Cd uptake is established, its mechanistic linkage with PSB-mediated phytoremediation remains poorly understood. This study employed Enterobacter sp. FM-1 and the Cd hyperaccumulator Solanum nigrum L. (S. nigrum L.) to elucidate how PSB regulate Cd accumulation through P cycling. Enterobacter inoculation significantly decreased soil pH and increased bioavailable Cd by 43.4 %-104.3 % relative to the control. The pH-driven mineralization of organic P was the primary process enhancing soil available P (AP), which rose by 12.1-32.2 %. Soil AP content was positively correlated with Cd concentrations in S. nigrum tissues, indicating a close association between enhanced phosphorus availability and plant Cd accumulation, accompanied by strengthened antioxidant defense related responses. Furthermore, PSB inoculation elevated phytochelatin levels via P-starvation response pathways, mitigating oxidative stress. Enhanced polyphosphate synthesis and phosphatase activity further promoted plant growth and P turnover. Metagenomic analysis revealed that Proteobacteria were the predominant carriers of P-cycling genes in the S. nigrum L. rhizosphere. Overall, Enterobacter sp. inoculation reshaped rhizosphere microbial communities, increased P bioavailability and improved Cd tolerance. These findings provide mechanistic insight into the coupling between microbial P activation and Cd uptake, offering a sustainable, microbially driven strategy for Cd-contaminated soil phytoremediation.