Bacterial community composition and biogeochemical heterogeneity in PAH-contaminated riverbank sediments

Predicting response of microbial communities to pollution requires an underlying understanding of the linkage between microbial community structure and geochemical conditions. Yet, there is scarce information about microbial communities in polycyclic aromatic hydrocarbons (PAH)-contaminated riverbank sediments. The aim of this study was to characterize bacterial communities in highly PAH-contaminated sediments and establish correlations between bacterial communities and environmental geochemistry of the sediments. Sediment core samples were collected from a highly PAH-contaminated site for (1) analysis of geochemical parameters including total nitrogen, total organic matter, moisture, total carbon, sulfate, pH, and PAH concentrations and (2) bacterial enumeration, 16S rDNA-based terminal restriction fragment length polymorphism analysis and sequencing. Non-metric dimensional scaling analyses revealed that bacterial community composition was strongly influenced by PAH concentration. Sulfate, organic matter, pH, and moisture were also related to community composition. A diverse microbial community was identified by the large number of operational taxonomic units recovered and by phylogenetic analyses. delta-Proteobacteria, firmicutes, and bacteriodetes were the dominant groups recovered. We also observed a high number of phylotypes associated with sulfate-reducing bacteria, some of which have been previously described as important in PAH degradation. Our study suggests that, despite intense pollution, bacterial community composition did exhibit temporal and spatial variations and were influenced by sediment geochemistry. Significant relationships between bacterial community composition and PAHs suggest that, potentially, extant microbial communities may contribute to natural attenuation and/or bioremediation of PAHs.