Persistent organic pollutants (POPs) accumulation in plants poses a risk to human health. POPs can be transported to plants through soil and air by abiotic or biotic processes. Their transport mechanisms in plants include symplastic and apoplastic processes, depending on the POP physicochemical properties and the vegetation species and growth stage. POPs with higher log octanol–water partition coefficient (Kow) values were absorbed more easily than those with lower logKow values. Specific endophytic bacteria showed increased expression of specific genes, more efficient degradation of organic contaminants, and the ability to degrade and reduce organic contaminants in host‐plant tissues. Several POP‐degrading endophytic bacteria were isolated from plants grown in POP‐contaminated soils and then inoculated successfully into plants. They expressed the genes encoding enzymes in the POP degradation pathways and reduced phytotoxicity and the amount of POP present in plant tissues. Thus, plant colonization by endophytic bacteria can be applied to degrading and reducing the concentration of POPs in plants.
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.
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