Identification of suspended particulate matters as the hotspot of polycyclic aromatic hydrocarbon degradation-related bacteria and genes in the Pearl River Estuary using metagenomic approaches.

Bacterial degradation is unequivocally considered as an important way for the cleanup of polycyclic aromatic hydrocarbon (PAHs) in the aquatic environment. However, the diversity and distribution of PAH-degrading bacterial communities and PAH degradation-related genes (PAHDGs) in ambient environment need to be investigated. In this study, bacteria in the water of the Pearl River Estuary (PRE) were initially separated as the particle-attached bacteria (PAB) and free-living bacteria (FLB), and were further characterized using metagenomic approaches. Proteobacteria (80.1 %) was identified as the most abundant PAH-degrading phylum in the PRE water, followed by Bacteroidetes, Actinobacteria, and Firmicutes. A substantial difference in the community structure was observed between PAH-degrading PAB and FLB. Both of PAH-degrading bacteria and PAHDGs were enriched on the suspended particulate matters (SPMs), with the range of enrichment factor (EF) from 7.84 × 104 to 6.64 × 106 (PAH-degrading bacteria) and from 1.14 × 103 to 1.76 × 105 (PAHDGs). The levels of PAH-degrading bacteria 16 S rRNA genes and PAHDGs on the SPMs were both significantly correlated with those in the aqueous phase (AP) in the PRE water (p < 0.05), indicating a dynamic distribution of PAH-degrading bacteria between these two phases. The total PAH concentrations on the SPMs of the PRE water were also significantly correlated with the total PAHDG levels in the PAB (p < 0.05). Our results suggested that the SPMs could be the important compartment for the elimination of PAHs from the aquatic environment.