Isolation And Performance Of Phenanthrene-Degrading Endophytic Bacterium Strains

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants in soil contaminated with crude oil, creosote, and coal tar. They are generated and dispersed into the environment by fossil fuel combustion, wood treatment processes, automobile exhaust, and waste incineration. The effect and fate of PAHs in soil is of great environmental and human health concern because of the carcinogenic, mutagenic, and teratogenic properties of PAHs, as well as their high concentrations and frequent observation in soil. PAHs and other organic chemicals accumulate in a variety of plant species. As the basis of human and animal food webs, plants could be routes by which harmful organic contaminants enter human and animal populations. Clearly, understanding the plant uptake of PAHs and reducing the plant PAH contamination are essential for assessment of both the exposure of humans and other animal species and the risk represented by PAH-contaminated sites.The objectives of this study were to isolate and characterize phenanthrene-degrading endophytic bacteria from plants grown in PAH-contaminated sites, and to elucidate the biodegradation of phenanthrene by the isolated functional microorganism under different environmental conditions. The main results were as follows:1. Two endophytic bacteria, which could degrade high concentration (up to200mg-L"1) of phenanthrene in liquid, were isolated from plants grown in PAHs-contaminated soils by selective enrichment culture. According to the results of morphology, physiology and the phylogenetical analyses of16S rDNA sequence, strain P1was identified as Stenotrophomonas sp., and strain P3was identified as Pseudomonas sp.. Strains P1and P3could grow well under20-35℃, the optimum culture temperature was30℃, and strain P1could tolerant higher temperature than strain P3. The optimum pH was7.0for strains P1and P3, and the growth was suppressed under higher or lower pH value. The two strains were able to grow well in culture with4%salinity. The two strains were of aerobic bacteria and could grow well under the inventory<40mL/100mL flask. The two strains showed different resistances to antibiotic, and strain P1had higher resistance compared to strain P3.2. The two strains could use phenanthrene as the sole carbon and energy. The degradation rate of phenanthrene (100mg·L-1) by strain P1and strain P3were90.2%and91.7%at28℃on the rotation shaker150r·min-1for7days. When cultivated under the conditions as:20-30℃, pH6.0-8.0,0%-4%concentration of NaCl,10-30mL/100mL inventory, the degradation rates of phenanthrene were inspected for two strains were greater than70%, and the optimum culture condition was:30℃, pH7.0, NaCl<4%, inventory≤30mL/100mL flask. Analyses on the phenanthrene degradation characteristics of two strains, it was concluded that tolerance to high temperature of strain P1was better than that of strain P3, while the tolerance of strain P3to pH variety and anoxic condition was better than that of strain P1.Strains P1and P3could degrade high concentrations of phenanthrene. At400mg·L-1phenanthrene, the degradation rates by strains P1and P3were50.2%and66.4%, respectively. Influence of different carbon sources and nitrogen sources in medium on the degradation rates of phenanthrene by strains P1and P3.were different. The optimal carbon and nitrogen sources of the two strains were different. Adding organic carbon and nitrogen sources into culture medium could enhance the degradation efficiency of the strains.3. Naphthalene, fluorene, pyrene, benzo (a) pyrene were chosen as representative PAHs in order to determinate the degradation characteristics of strains P1and P3under single and combined pollution of PAHs. The results showed that, to single pollution, strain P3could degrade naphthalene, fluorene, pyrene, benzo (a) pyrene, and the degradation rates were99.7%,91.5%,54.6%,14.4%, respectively. Strain P1could degrade naphthalene, fluorene, pyrene except benzo (a) pyrene, and the degradation rates were99.8%,88.0%,51.2%respectively, but could not degrade benzo (a) pyrene. Under combined pollution of PAHs, the degradation rates of naphthalene and fluorene had no significant difference from single PAH pollution, while the degradation rates of pyrene decreased15.0%and6.0%, respectively. Strain P1could not degrade benzo (a) pyrene, while the degradation rate of benzo (a) pyrene of strain P3increased significantly to33.8%.