Résumé
Interactions between the plant and its microbialcommunities in the rhizosphere control microbial polycyclic aromatic hydrocarbons (PAH) biodegradation processes. Arbuscular mycorrhizal (AM) fungi can influenceplant survival and PAH degradation in polluted soil. Thiswork was aimed at studying the contribution of themycorrhizosphere to PAH biodegradation in the presenceof ryegrass (Lolium perenne L., cv. Barclay) inoculatedwith Glomus mosseae (BEG 69) by taking into account thestructure and activity of bacterial communities, PAHdegrading culturable bacteria as a function of the distancefrom roots. Ryegrass was grown in compartmentalizedsystems designed to harvest successive sections of rhizosphere in lateral compartments polluted or not withphenanthrene (PHE). Colonization of roots by G. mosseae(BEG 69) modified the structure and density of bacterialpopulations in the mycorrhizosphere, compared to therhizosphere of non-mycorrhizal plants. G. mosseae increased the density of culturable heterotrophic and PAHdegrading bacteria beyond the immediate rhizosphere inthe presence of PHE, and increased the density of PAHdegraders in the absence of the pollutant. Biodegradationwas not significantly increased in the mycorrhizosphere,compared to control non-mycorrhizal plants, where PHEbiodegradation already reached 92% after 6 weeks. However, dioxygenase transcriptional activity was found to behigher in the immediate mycorrhizosphere in the presence ofG. mosseae (BEG 69).