Abstract: Endophytic bacteria reside within plant hosts and have a close symbiotic association with host plants. Their excellent properties in heavy metal absorption,tolerance and detoxification provide a novel approach for the remediation of contaminated soil by heavy metals. This review concentrates on the fundamental mechanism of endophyte-assisted phytoremediation of heavy metal-contaminated soils,including the promoting the growth of host plants under heavy metals by producing plant growth regulating hormone and secreting ACC deaminases and chitinase and so on,reducing the damages of heavy metals to plants by altering the bioavailability /or toxicity of heavy metal,and improving the resistance of plants to heavy metal stress by forming joint remediating complex. Then recent progress in characterizing the diversity of endophytic bacteria from hyperaccumulator and its influencing factors are also reviewed. Furthermore,the main factors influencing the effect of endophytic bacteria in the phytoremediation are discussed,including the source and activity of endophytic bacteria and various biotic and abiotic factors of environmental stress. Special attention is paid to the future study in the field of endophyte-assisted phytoremediation technology,such as the mechanism of endophytic bacteria’s own survival and how to tolerate heavy metals,behavioral dynamics and metabolism of endophytic bacteria,and the ecological interaction between endophytic bacteria,plants and soil will be considered,aiming at promoting the large-scale application of endophytic bacteria in the phytoremediation of heavy metal-contaminated soil.

Key words: endophytic bacteria, heavy metal, remediation mechanism