Evolution of Functional Bacteria in a Polycyclic Aromatic Hydrocarbon (PAH)-Degrading Bioreactor

In this study a laboratory-scale sequencing batch bioreactor was constructed, using phenanthrene/pyrene as the sole carbon-source, to demonstrate the removal efficiencies of polycyclic aromatic hydrocarbons (PAHs) and the evolution process of a functional bacterial community. The removal rates were: COD, 51.4 to 76.3%; phenanthrene, 63.5 to 92.4%; and pyrene, 65.9 to 90.1%. Quantification analysis indicated that in sludge samples from the phenanthrene/pyrene degradation stage, the contents of 16S rRNA and ring-hydroxylating dioxygenase genes of Gram-positive and Gram-negative bacteria were 10-and 72-, 102- and 1152-, 31- and 905-fold higher, respectively, than those in seed sludge samples. Clone sequencing and evolution analysis showed that genera Comamonas, Pseudomonas, and Mycobacterium were distributed across all samples and were significant PAH-degrading populations, but some genera, such as Polaromonas and Nocardioides, were substantially enriched only when phenanthrene/pyrene was fed. Correspondingly, the functional genes nidA3, phnAc, and ndoC2 were distributed across all samples, whereas nagAc, pdoA2, and pdoA were enriched only when phenanthrene/pyrene was fed.