Effect Of Arbuscular Mvcorrhizal Fungi On Remediation Of Polvchlorinated Biphenvls Contaminated Soil And Its Mechanisms

Remediation of polychlorinated biphenyls (PCBs) contaiminated soils has been of great concern wordwide since the PCBs are persistent, bioaccumulate and carcinogenic. Arbuscular mycorrhizal (AM) fungi play a key role in the functioning of terrestrial ecosystems, and have been found very important in bioremediation of soil contaminated with organic pollutants. To investigate the mechanisms of PCBs remediation by AM fungi, greenhouse experiments were introduced to study the influence of different cucurbits and AM fungi on soil PCBs dissipation and microbial community variation. Stable Isotope Probing and Illumina Miseq sequencing technique were also applied to find the PCB degradation microorganisms which related to AM fungi hyphae.(1) Three Cucurbita species (C. pepo L. cv. Black Beauty, C. moschata Duch. cv. Miben, C. maxima Duch cv. Cuili 1) and one Cucumis speices (C. sativus L. cv. Jinyou 2) were selected to study their effects on remediation of long-term PCBs contaminated soils and related mechanisms. Results showed that compared to the non-planted control, soil PCBs dissipation rates increased significantly in all treatments, among which C. pepo and C. moschata treatments were more effective than the other two treatments (P<0.05). C. pepo and C. moschata treatments had similar soil microbial community and PCB congener profile compositions. G-bacterial PLFA correlated with total PCB dissipation rate (R2=0.719, P<0.001), while G- bacterial and fungal PLFA correlated with pentachlorinated biphenyls dissipation rate (R2=0.590, P<0.01). The results indicated that the tested plants of C. pepo and C. moschata can play important roles in PCBs remediation through altering soil microbial community composition.(2) In a pot experiment, C. pepo was slected as the host plant to test effects of different AM fungi (Acaulospora laevis, Glomus caledonium, and Glomus mosseae) on soil Aroclor 1242 dissipation and their mechanisms. In comparison with the non-inoculated control, soil Aroclor 1242 dissipation rates and bacterial abundance were significantly higher in A. laevis and G. mosseae treatments (P<0.05). AM fungi have great positive effect on genes encoding biphenyl dioxgenase (bphA) and Rhodococcus-like 2,3-dihydroxybiphenyl dioxygenase (bphC) when compared to the control (P<0.05). Betaproteobacteria and Actinobacteria dominated in soil microbial community, in which Actinobacteria contributed significantly to the variation of PCB congener profile compositions in the bulk soil (P<0.05). The results indicated that A. laevis and G. mosseae could enhance soil PCBs dissipation rate through promoting soil bph gene and specific microbial groups’ abundance.(3) A two-compartment rhizobox system was used to assess the quantitative effects of AMF hyphae on the soil microbial community and Aroclor 1242 dissipation. Total soil PCB dissipation rates in the AM fungi inoculation treatments were significantly higher than that in the control (P<0.05). The dissipation rates of tri-and tetrachlorinated biphenyls, and total PCBs, were all significantly correlated with soil hyphal length (P<0.05). The Rhodococcus-like bphC gene was found responded positively to AM fungi (P<0.05). Phylogenetic analyses indicated that AM fungal hyphae altered the bacterial community composition. The classes Betaproteobacteria and Actinobacteria were dominant in the soil, while Burkholderials and Actinomycetales were dominant at the order level. Our results suggest that both of the AM fungal hyphal exudates and the hyphae per se had quantitative effects on shaping the soil microbial community structure and promoting bphC(Rh) gene abundance, and could consequently modify PCB dissipation processes.(4) DNA-based stable isotope probing in combination with Illumina Miseq Sequencing was used to identify members of the microbial community that metabolize [13C] PCB-4 in the hyphosphere of G. mosseae. Both bphA and Rhodococcus-like bphC gene were significant increased in [C] labled DNA in the control, while AMF hyphae only enhanced [13C] bphC gene abundance (P<0.05). AM fungal hyphae greatly altered soil microbial community composition, as well as PCB-4 utilizing bacteria. The relative proportion of phylae Firmicutes and Proteobacteria in [13C] labled DNA was promoted by AM fungal hyphae, especially for the class Betaproteobacteria (P<0.05). Furthermore, our results indicated that order Burkholderiaceae was the major [13C] PCB-4 utilizing bacteria, and was significantly enhanced by AM fungal hyphae.