A phenanthrene-degrading endophytic bacterium,Pn2,was isolated from Alopecurus aequalis Sobol grown in PAH-contaminated soils.Based on morphology,physiological characteristics and the 16S rRNA gene sequence,it was identified as Massilia sp..Strain Pn2 could utilize phenanthrene as the sole carbon source for growth,and it degraded more than 95%of the phenanthrene(150 mg·L-1)in a minimal salts medium within 48 hours at an initial pH of 7.0 and a temperature of 30C.The addition of C or N sources to the medium effectively promoted bacterial growth and phenanthrene degradation.Strain Pn2 could utilize a series of other PAH,including naphthalene,acenaphthene,anthracene and pyrene,as the sole carbon source for growth and degrade them to different degrees.Meanwhile,it could colonize the root surface of ryegrass(Lolium multiflorum Lam),invade its internal root tissues and translocate into the plant shoot.Phenanthrene concentrations in ryegrass roots and shoots were reduced by 54%and 57%,respectively,when treated with the endophyte Pn2.This is the first report of a phenanthrene-degrading endophytic bacterial isolate.Strain Pn2 could be a novel and useful bacterial resource for eliminating plant PAH contamination in polluted environments by degrading PAH inside plants.Furthermore,we provide new perspectives on the control of plant uptake of PAH by endophytic bacteria.