Responses of endophytic and rhizospheric bacterial communities of salt marsh plant (Spartina alterniflora) to polycyclic aromatic hydrocarbons contamination

Plants and their root-associated microbes play important roles in the remediation of polycyclic aromatic hydrocarbons (PAHs) present in the sediments of contaminated coastal wetlands. The detailed information about the effects of PAHs on root-associated bacterial communities could help to isolate PAH-degrading bacteria and optimize the process of phytoremediation. The community structures of rhizospheric (RB) and endophytic bacteria (EB) of salt marsh plant (Spartina alterniflora) grown in phenanthrene (PHE)- and pyrene (PYR)-contaminated sediments (for 70 days) were investigated using the barcoded Illumina paired-end sequencing technique. The diversity and community structure of EB and RB were more sensitive to PHE and PYR contamination as compared to those in the sediments. All samples were strongly clustered according to EB, RB, and sediments, suggesting the niche-specific influence of PAHs on bacterial communities. Potential PAH-degrading bacteria (Pseudomonas sp., Paenibacillus sp., and Flavobacterium sp.) in EB and RB were stimulated by PAH contamination. The results revealed an increase prevalence of specific bacteria which may be responsible for PAH degradation. PHE contamination increased the abundance of Proteobacteria in EB but decreased the number of Firmicutes, Bacteroidetes, and Chloroflexi. The numbers of Proteobacteria and Firmicutes in EB were enhanced by PYR treatment. However, both PHE and PYR treatment showed similar effects on the bacterial communities in RB. The results suggested that PAH pollution could alter root-associated bacterial communities of S. alterniflora, whose EB might play an important role in the phytoremediation of PAH-contaminated sediments.