Screening of manganese-resistant bacteria and their synergistic effect with Koelreuteria paniculata on remediation of manganese-contaminated soil

• Bacillus cereus and Priestia megaterium contain hydroxyl and phosphate groups that interact with manganese ions. • Inoculation with Bacillus cereus enhanced the biomass, net photosynthetic rate and stomatal conductance of Koelreuteria paniculata . • Inoculation with Priestia megaterium enhanced superoxide dismutase and catalase activities of Koelreuteria paniculata . • Inoculation with Priestia megaterium increased the leaf manganese content of Koelreuteria paniculata . • Inoculation with Bacillus cereus significantly enhanced the Mn accumulation and bioconcentration factor. Plant-microbe collaborative remediation is a highly promising heavy metal remediation strategy. However, its remediation efficiency for manganese (Mn) tailings and its underlying mechanism remain inadequately explored. This study aimed to screen microbial strains capable of remediating Mn contamination and evaluate the potential of these strains to enhance the remediation of heavy metal-contaminated soils through plant–microbe interactions. A bacterial strain with both Mn resistance and plant growth-promoting characteristics was isolated from the rhizosphere of plants in Mn tailings. Pot experiments were conducted to inoculate 2-year-old Koelreuteria paniculata seedlings grown in non-polluted soil and in Mn tailings. The effectiveness of the strain in remediating Mn-polluted soil was evaluated using indicators such as its growth, photosynthetic characteristics, antioxidant enzyme activity, Mn accumulation capacity of K. paniculata , and overall soil remediation effect. This study identified two Mn-resistant bacteria including Bacillus cereus (EA-1) and Priestia megaterium (BN-4). Fourier transform infrared spectroscopy (FTIR) identified crucial functional groups on the bacterial surface, such as hydroxyl and phosphate groups, which play a key role in Mn adsorption. In Mn tailings, inoculation with the BN-4 strain significantly increased superoxide dismutase (SOD) and catalase (CAT) activities in the leaves of K. paniculata by 201.57% and 34.48%, respectively, compared to the uninoculated treatment. However, inoculation with the EA-1 strain enhanced the root, stem, and leaf biomass, net photosynthetic rate, stomatal conductance, Mn accumulation, and bioconcentration factor (BCF) of K. paniculata by 72.70%, 47.82%, 51.32%, 81.38 %, 86.05%, 113.09% and 76.19%, respectively, compared to the uninoculated treatment. Considering the growth of K. paniculata and its capacity for Mn accumulation and BCF, inoculation with the EA-1 strain is a more favorable approach for remediation of Mn tailings.