Exogenous inoculation with heavy metal-immobilizing bacteria roused the key rhizosphere bacterial community and metabolites of wheat to inhibit cadmium absorption

Rhizosphere functional microorganisms play an important role in the bioremediation of heavy metal-polluted farmlands, however, further research is needed to investigate the effects of exogenous inoculation of functional strains on key bacterial communities and metabolites in cadmium (Cd)-polluted wheat farmlands. This study investigated the effects of the urease-producing bacterium Enterobacter bugandensis TJ6 combined with polyamine-producing bacterium Serratia marcescens X43 on Cd uptake by wheat and its microbiological and soi biolological mechanisms. The results showed that strains TJ6+X43 reduced (95.1 %) the Cd content by secreting urease and polyamines and inducing the precipitation of Cd to form CdCO3 and Cd(OH)2. The combined strains increased (22.7 %) the dry weight and reduced (37.2 %) the Cd content in wheat grains. Moreover, the DTPA-Cd content, the NH4+/NO3- ratio and the urease activity were increased in the presence of strains TJ6+X43. The combined strains reduced the diversity of bacterial communities, but increased the relative abundances of key strains such as Gemmatimonas, Ramlibacter, Sporacetigenium, Pseudomonas, Microvirga, and Nitrospira in the wheat rhizosphere soil. In addition, the contents of glutamate, glutathione, L-ribulose, arginine, nitrite, spermine, isocitrate, and D-xylulose were also increased. More importantly, glutamate metabolism was roused to induce rhizosphere metabolites and functional bacterial communities to synergistically inactivate Cd. The results showed that inoculation with heavy metal-immobilizing bacteria can result in the activation of key functional bacteria and the regulation of metabolite production in wheat rhizosphere soil to immobilize heavy metals, which has broad potential in the bioremediation of wheat fields and ensuring food security.