Plant growth-promoting bacteria and nanomaterials synergism to enhance Lolium perenne growth and phytoremediation in cadmium-contaminated soil

•GNPs-Serratia sp combination enhanced ryegrass biomass and Cd uptake in the plant.•Cd uptake in ryegrass was positively correlated with bacterial colonization in soil.•PGPB increased enzyme activity in the soil and reduced stress injury to ryegrass.•g-C3N4 and GNPs increased residual Cd fraction in soil and reduced its toxicity. Innovative integrated approaches of nanoparticles (NP) and plant growth-promoting bacteria (PGPB) can accelerate plant growth and remediation of cadmium (Cd) contaminated soil. The effectiveness of the combination and interactions amongst Cd-resistant PGPB, ryegrass (Lolium perenne), graphene nanoplatelets (GNPs), and graphitic carbon nitride (g-C3N4) nanomaterials have not yet been elucidated. Cd-spiked soil was supplemented with GNPs, g-C3N4, and inoculated with bacterial strains (Serratia bozhouensis and Serratia marcescens). The PGPB and GNPs combination produced the highest biomass, enhancing the accumulation of Cd in ryegrass. The highest Cd uptake (92 %) by ryegrass was observed in Serratia bozhouensis and GNPs treatments. The reasons for increased plant growth and Cd-phytoremediation by the PGPB-GNPs combination are explained. GNPs application promoted PGPB survival in the rhizosphere. Inoculant strains showed a high relative abundance of >82 % in the inoculated treatments. The exchangeable Cd fraction significantly increased in PGPB-GNPs treatments. The highest exchangeable Cd (80 %) was noted with Serratia bozhouensis and GNPs. PGPB also increased the dehydrogenase, catalase, phosphatase, and urease enzyme activity in soil. The PGPB-GNPs combination also reduced the Cd-induced stress injury to ryegrass through increased production of antioxidants. The present work supports our understanding of the synergistic effects of nanomaterials, bacteria, and plants, thus boosting their role in restoring heavy metal-contaminated soils. [Display omitted]