Abstract
A phenanthrene-degrading endophytic bacterium, Pn2, was isolated from Alopecurus aequalis Sobol grown in soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Based on morphology, physiological characteristics and the 16S rRNA gene sequence, it was identified as Massilia sp. Strain Pn2 could degrade more than 95% of the phenanthrene (150 mg·L−1) in a minimal salts medium (MSM) within 48 hours at an initial pH of 7.0 and a temperature of 30°C. Pn2 could grow well on the MSM plates with a series of other PAHs, including naphthalene, acenaphthene, anthracene and pyrene, and degrade them to different degrees. Pn2 could also colonize the root surface of ryegrass (Lolium multiflorum Lam), invade its internal root tissues and translocate into the plant shoot. When treated with the endophyte Pn2 under hydroponic growth conditions with 2 mg·L−1 of phenanthrene in the Hoagland solution, the phenanthrene concentrations in ryegrass roots and shoots were reduced by 54% and 57%, respectively, compared with the endophyte-free treatment. Strain Pn2 could be a novel and useful bacterial resource for eliminating plant PAH contamination in polluted environments by degrading the PAHs inside plants. Furthermore, we provide new perspectives on the control of the plant uptake of PAHs via endophytic bacteria.
Highlights
Anthropogenic soil contamination has become a worldwide environmental problem in recent decades [1]
3.1 Isolation and identification of strain Pn2 A phenanthrene-degrading endophytic bacterium, Pn2, was isolated from the root interiors of Alopecurus aequalis Sobol grown at a polycyclic aromatic hydrocarbons (PAHs)-contaminated site
It was reported that the strain Burkholderia fungorum DBT1, isolated from sediment and capable of degrading PAH compounds such as naphtalene, phenanthrene and dibenzothiphene, was able to colonize internal roots of poplar and increase the plant phytodegradation capability once grown in presence of the above mentioned PAHs [36]
Summary
Anthropogenic soil contamination has become a worldwide environmental problem in recent decades [1]. In the range of 0– 296 mg?L21, low concentrations (#74.0 mg?L21) of Brij (polyethylene glycol dodecyl ether, a nonionic surfactant) generally enhanced plant uptake and the accumulation of phenanthrene and pyrene, whereas Brij at relatively high concentrations ($ 148 mg?L21) markedly restricted the plant uptake of these PAHs [11]. At concentrations generally lower than 13.2 mg?L21, Tween 80 (polyoxyethylenesorbitan monooleate, a nonionic surfactant) enhanced the plant uptake of phenanthrene and pyrene; when present at higher concentrations (13.2–105.6 mg?L21), Tween 80 inhibited the uptake of both PAH compounds in the test plant [12]. Compared with chemical surfactant-dependent technology, the biodegradation of PAHs inside plants is more environmentally friendly; the control of PAH accumulation in plants with endophytes has attracted considerable interest in recent years [14]
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