The Study On The Degradation Of Phenanthrene By Endophytic Fungus

Phenanthrene is a three-ring polycyclic aromatic hydrocarbon. Among PAHs phenanthrene was selected because it is one of the most abundant PAHs in the environment, there have been many studies used phenanthrene as model PAHs for the investigation of degradation by different fungi and bacteria. This study screened phenanthrene-degrading filamentous fungi from endophytic fungus which utilized lignin as their carbon source. Then endophytic fungus showed phenanthrene degradation ability was co-cultured with its host plant, Monitoring the phenanthrene degradation and plant reaction to the phenanthrene. At last, the phenanthrene degradation mechanism by endophytic fungus was discussed.Our previous study isolated some endophytic fungi which utilized lignin as their carbon source. Based on this research, the present study screened phenanthrene-degrading filamentous fungi from the isolated endophytic fungi. The results showed that endophytic fungus B3 (Phomopsis sp.) and Y17 (Ceratobasidumi sp.) had phenanthrene degradation ability. The degradation rate reached 2.95 mg/d and 8.23 mg/d, respectively. Compared with the other screened phenanthrene degrading fungi and some white rot fungi which had been used in the PAHs biodegradation, the degradation rate of phenanthrene by B3 and Y17 were relatively high. This result indicated that B3 and Y17 might be a potential candidate for an effective bioremediation of PAHs contamination. To our knowledge, this is the first report on PAHs degradation by endophytic fungus. In addition, this is also the first report of Phomopsis sp. and Ceratobasidumi sp. that showed ability in degrading PAHs. The present results confirmed our hypothesis that some endophytic fungi might have the ability to degrade PAHs.Degradation of phenanthrene by B3 (Phomopsis sp.) in different conditions were studied. The results showed that lactose as the carbon source, peptone as nitrogen source, 10g/L respectively facilitated the degradation of phenanthrene. Guaiacol acted as inducer on the phenanthrene degradation. After 10 days rotary culture, the degradation rate of phenanthrene (100mg/L) reached 52.54%. No apparent correlation between degradation percentage and the tested ligninolytic enzyme. In addition, B3 was able to tolerate higher concentrations of phenanthrene at the concentration of 500 mg/L.Previous results showed that the endophytic fungus B3 had a reciprocal relationship with the paddy rice. In this paper, when B3 was co-culture with paddy rice, synergetic effect was occurred on the degradation of phenanthrene. Meanwhile, B3 decreased the injury of paddy rice under the condition of phenanthrene stress.The mechanism of phenanthrene degradation by endophytic fungus Y17 was studied. Among extracellular ligninolytic enzyme activities tested, MnP was the predominant ligninolytic enzyme and its production was greatly induced in the presence of phenanthrene. To confirm the involvement of MnP in phenanthrene degradation, the promotion and inhibition studies on MnP by different concentration of Mn²⁺ and NaN₃ were performed. Additionally, fungi mycelium free and resuspended experiments were carried out. The obtained results showed no apparently connection between MnP activity and phenanthrene degradation. While the mycelium and fresh medium were the crucial factors affecting the oxidation of phenanthrene. After phenanthrene was degraded by Y17, the products were analyzed by GC-MS. The result showed that Y17 may have two or more pathways for phenanthrene degradation. However, more work is needed to get the further information of phenanthrene degradation by endophytic fungus.