Bacterial community and PAH-degrading genes in paddy soil and rice grain from PAH-contaminated area

The significance of the bacterial communities and PAH-degrading genes (PDGs) in PAH-contaminated soil has received extensive attention, however, little attention was focused on those in plants grown on contaminated farmland soil. This study aimed to dissect the interactive relationships among PAHs, PDGs, and bacterial communities in the rhizosphere soil and rice grain. Although the concentrations and compositions of PAHs varied greatly, PAHs was the most critical factor in shifting of community in the soil and rice grain. Diversity of the potential PAH-degrading bacteria (PDB) in the rhizosphere soil was higher than that in the rice grain; however, the relative and absolute abundances of PDB in the rhizosphere soil were lower than those in the rice grain. Abundances of four PDGs in the soil were higher than those in the rice grain, and many species of bacteria, including Pseudomonas, Sphingomonas, and so on, which may harbor PDGs were detected. Bacteria in the soil had stronger relationships and were more centrally clustered within the network compared to bacteria in the rice grain. The keystone species (Actiobacteria, Betaproteobacteria, and Chloroflexi) in the soil were different from those (Pseudomonas, Sphingomonas, and Comamonadaceae) in the rice grain. Pseudomonas and Sphingomonas in the rice grain seemed to be the most important bacteria associated with PAH degradation. Overall, these findings provided novel insights into bacterial communities and PDGs in both the soil and plant from the PAH-contaminated paddy soil.