Defined and natural PAH contaminations shift PAH-degrading bacterial community in rhizosphere of ornamental plant species Echinacea purpurea L.

Abstract

The native microorganisms in the plant rhizosphere are considered to be predominant contributors to the phytoremediation of polycyclic aromatic hydrocarbon (PAH). In this study, the influence of a fresh defined PAH mixture at different concentrations (P25, P50, and P100) or an aged natural PAH mixture from an oilfield site with history for more than 30 years (POF) on bacterial communities and their potential to degrade PAHs in the Echinacea purpurea L. rhizosphere were investigated based on 16S rRNA amplicon sequencing and functional gene prediction with PICRUSt2. Result shows that regardless of the PAH concentration or aging time, the enrichment of most members of Actinobacteria and Patescibacteria and their lineages in the E. purpurea rhizosphere is associated with the enhancement of PAHs’ degradation potential. Mycobacterium sp. and Saccharimonadaceae sp. predominated, especially in P100, whereas potential degraders, such as Streptomyces sp. and Bacteroides sp. prevailed in POF. Consistent with the PAH removal rate (80.0%, 77.0%, 38.0%, and 35.5% in P25, P50, P100, and POF, respectively), the abundance of PAH-degrading functional genes, including nidABD, pdhEFGHIJK, and phtAaAbAcAdBC, increased and aided in the PAH degradation process, especially in P25, whereas the abundance of nahE increased only in the POF. The available soil nutrients and pH were also key environmental factors that shaped PAH-degrading bacterial community in E. purpurea rhizosphere. This work brings some new insights into the shifts in bacterial diversity, structure, and PAH-degrading function in E. purpurea rhizosphere to different PAH contaminations, which could help select the most suitable protocols for PAH phytoremediation.