Abstract
Some root-associated bacteria could degrade polycyclic aromatic hydrocarbons (PAHs) in contaminated soil; however, their dynamic distribution and performance on root surface and in inner plant tissues are still unclear. In this study, greenhouse container experiments were conducted by inoculating the phenanthrene-degrading bacterium Diaphorobacter sp. Phe15, which was isolated from root surfaces of healthy plants contaminated with PAHs, with the white clover (Trifolium repens L.) via root irrigation or seed soaking. The dynamic colonization, distribution, and performance of Phe15 in white clover were investigated. Strain Phe15 could efficiently degrade phenanthrene in shaking flasks and produce IAA and siderophore. After cultivation for 30, 40, and 50 days, it could colonize the root surface of white clover by forming aggregates and enter its inner tissues via root irrigation or seed soaking. The number of strain Phe15 colonized on the white clover root surfaces was the highest, reaching 6.03 Log CFU⋅g–1 FW, followed by that in the roots and the least in the shoots. Colonization of Phe15 significantly reduced the contents of phenanthrene in white clover; the contents of phenanthrene in Phe15-inoculated plants roots and shoots were reduced by 29.92–43.16 and 41.36–51.29%, respectively, compared with the Phe15-free treatment. The Phe15 colonization also significantly enhanced the phenanthrene removal from rhizosphere soil. The colonization and performance of strain Phe15 in white clove inoculated via root inoculation were better than seed soaking. This study provides the technical support and the resource of strains for reducing the plant PAH pollution in PAH-contaminated areas.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent toxic organic pollutants that exist widely in the soil environment (Falciglia et al, 2016)
In Delhi, India, the total PAH contents hidden in PM10 and PM2.5 in winter were as high as 177.5 ng·m−3, and these PAHs would enter the soil eventually (Singh et al, 2011)
The colonies of strain Phe15 are milky white with neat edges and smooth and moist surfaces (Figure 1B)
Summary
Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent toxic organic pollutants that exist widely in the soil environment (Falciglia et al, 2016). PAHs are mainly derived from the incomplete combustion of petroleum, coal, wood, and other organic matter (Abdel-Shafy and Mansour, 2016). Studies have shown that the main source of PAHs has changed from the incomplete. It can be seen that manmade production activities have become the main source of PAHs released into the environment. A study performed in 2011 found that the petroleum refining soil in Bratislava contained up to 2000 μg·Kg−1 of PAHs (Musa Bandowe et al, 2011). To make matters worse, recent studies have shown an increase in PAHs over the Arctic (Yu et al, 2019). PAHs in the soil can be taken up and accumulated by plants and transferred and biomagnified through the food chains, threatening human health (Gao et al, 2013). It is of great significance to regulate the absorption and accumulation of PAHs in soil by plants, to reduce the PAH contamination in crops and produce safe agricultural products in PAH-contaminated areas
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