Indigenous PAH degraders along the gradient of the Yangtze Estuary of China: Relationships with pollutants and their bioremediation implications

This study investigated the network of polycyclic aromatic hydrocarbon (PAH) degraders in the Yangtze estuarine and coastal areas. Along the estuarine gradients, Proteobacteria and Bacteroidetes were the dominant bacterial phyla, and forty-six potential PAH degraders were identified. The abundance of genes encoding the alpha subunit of the PAH-ring hydroxylating dioxygenases (PAH-RHDα) of gram-negative bacteria ranged from 5.5 × 10⁵ to 5.8 × 10⁷ copies g⁻¹, while that of gram-positive bacteria ranged from 1.3 × 10⁵ to 2.0 × 10⁷ copies g⁻¹. The PAH-degraders could represent up to 0.2% of the total bacterial community and mainly respond to PAHs and Cu concentrations, which indicate anthropogenic activities. Salinity and pH showed negative regulating effects on the PAH-degrading potential and the tolerance of bacteria to pollutants. PAH degraders such as Novosphingobium and Mycobacterium exhibit heavy-metal tolerance and core roles in the network of PAH degraders. These outcomes have important implications for bioremediation.