title: Biodegradation of Mixed PAHs by PAH-Degrading Endophytic Bacteria.
abstract: Endophytic bacteria can promote plant growth, induce plant defence mechanisms, and increase plant resistance to organic contaminants. The aims of the present study were to isolate highly PAH-degrading endophytic bacteria from plants growing at PAH-contaminated sites and to evaluate the capabilities of these bacteria to degrade polycyclic aromatic hydrocarbons (PAHs) in vitro, which will be beneficial for re-colonizing target plants and reducing plant PAH residues through the inoculation of plants with endophytic bacteria. Two endophytic bacterial strains P₁ (Stenotrophomonas sp.) and P₃ (Pseudomonas sp.), which degraded more than 90% of phenanthrene (PHE) within 7 days, were isolated from Conyza canadensis and Trifolium pretense L., respectively. Both strains could use naphthalene (NAP), PHE, fluorene (FLR), pyrene (PYR), and benzo(a)pyrene (B(a)P) as the sole sources of carbon and energy. Moreover, these bacteria reduced the contamination of mixed PAHs at high levels after inoculation for 7 days; strain P₁ degraded 98.0% NAP, 83.1% FLR, 87.8% PHE, 14.4% PYR, and 1.6% B(a)P, and strain P₃ degraded 95.3% NAP, 87.9% FLR, 90.4% PHE, 6.9% PYR, and negligible B(a)P. Notably, the biodegradation of PAHs could be promoted through additional carbon and nitrogen nutrients; therein, beef extract was suggested as the optimal co-substrate for the degradation of PAHs by these two strains (99.1% PHE was degraded within 7 days). Compared with strain P₁, strain P₃ has more potential for the use in the removal of PAHs from plant tissues. These results provide a novel perspective in the reduction of plant PAH residues in PAH-contaminated sites through inoculating plants with highly PAH-degrading endophytic bacteria.
authors: Institute of Organic Contaminant Control and Soil Remediation, College of Resource and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China. zhuxuezhu@njau.edu.cn.
authors: Xuezhu
authors: X
authors: Zhu
authors: Institute of Organic Contaminant Control and Soil Remediation, College of Resource and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China. nixue@bgechina.cn.
authors: Xue
authors: X
authors: Ni
authors: Institute of Organic Contaminant Control and Soil Remediation, College of Resource and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China. mgatheru94@gmail.com.
authors: Michael Gatheru
authors: MG
authors: Waigi
authors: Institute of Organic Contaminant Control and Soil Remediation, College of Resource and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China. liujuan@njau.edu.cn.
authors: Juan
authors: J
authors: Liu
authors: Institute of Organic Contaminant Control and Soil Remediation, College of Resource and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China. 2013203015@njau.edu.cn.
authors: Kai
authors: K
authors: Sun
authors: Institute of Organic Contaminant Control and Soil Remediation, College of Resource and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China. gaoyanzheng@njau.edu.cn.
authors: Yanzheng
authors: Y
authors: Gao
mesh_terms: D001419:Bacteria / Q000302:isolation & purification; D001673:Biodegradation, Environmental; D060026:Endophytes / Q000302:isolation & purification / Q000378:metabolism*; D066298:In Vitro Techniques; D010944:Plants / Q000378:metabolism; D011084:Polycyclic Aromatic Hydrocarbons / Q000378:metabolism*
chemical_list: D011084:Polycyclic Aromatic Hydrocarbons
keywords: 16S rRNA gene; Pseudomonas sp.; Stenotrophomonas sp.; biodegradation; endophytic bacteria