PAH degradation and gene abundance in soils and vegetables inoculated with PAH-degrading endophytic bacteria

Abstract

Inoculation with PAH-degrading endophytic bacteria effectively reduces the polycyclic aromatic hydrocarbon (PAH) contents in plants grown in contaminated sites. However, the degradation capacity of a single bacterium on various PAHs is limited. In this study, a composite of six PAH-degrading endophytic bacterial strains (CEB) was constructed, which was capable of degrading 16 USEPA priority PAHs. The ∑PAH contents in the shoots and roots of water spinach, Chinese cabbage, and pakchoi with CEB inoculation were reduced by more than 46% and 51%, respectively, while those in the corresponding vegetated soils were reduced by more than 32%. Moreover, the abundances of PAH catabolic genes (nidA, bphA1f, and phe) in the vegetables all increased after inoculation with CEB, and the abundances of the nidA and bphA1f genes increased tens or even hundreds of times, especially compared with those in uninoculated vegetables. The abundances of these genes in the corresponding vegetated soils also increased, which might be responsible for the corresponding reduction in PAH contents. This study confirmed that inoculating CEB can effectively increase the abundances of PAH catabolic genes and thus reduce the PAH contents in vegetated soils and plants. The findings of this study support the application of CEB to remove PAHs from soils and plants.