Investigation of the Coupling Mechanism Between Naphthalene Degradation and Denitrification of a Naphthalene Degraded Bacterial Consortium Under Denitrification

To investigate the coupling mechanism between naphthalene degradation and denitrification using a liquid media containing naphthalene (sole carbon source) and nitrate, a naphthalene degradation bacterial consortium under denitrification was enriched from a soil with potential risk of PAH (polycyclic aromatic hydrocarbon) contamination. The bacterial community composition of the enriched consortium was analyzed by Illumina MiSeq Sequencing. Subsquently, the enriched consortium was cultured under anaerobic conditions for 9 days, and the concentrations of electron acceptors (nitrate and nitrite) for denitrification, gaseous reduction products (N2O and N2) involved in denitrification, and abundances of denitrification concerned genes (narG:periplasmic nitrate reeducates gene; nirS:cd1-nitrite reductase gene) were detected at days 1, 3, 7, and 9. The result of Illumina MiSeq Sequencing showed that Pseudomonas (Proteobacteria) was the most dominant genus in this enriched consortium. Under anaerobic conditions, the naphthalene removal rate of this enriched consortium was 49.11% within 9 days. Relative higher naphthalene degradation rates were found both at the beginning (day 1-3) and the end (day 7-9) of incubation, and these were significantly higher than at the middle (day 3-7) of the incubation stage (P<0.05). The concentration of nitrate decreased during the whole culture period, while the concentration of nitrite increased during the initial incubation (day 1-3) and rapidly decreased from day 3 to 9. Furthermore, obvious productions of N2O[3.39 μg ·(L ·h)-1] and N2[8.97 μg ·(L ·h)-1] were only measured at the end of incubation (day 7-9). The abundances of both narG and nirS increased during the incubation, indicating the continuous growth of denitrifiers in the enriched consortium during the incubation period. In summary, this study illustrated that both the nitrate reducing stage and gas producing steps of denitrification could be coupled with anaerobic naphthalene degradation, which might be helpful for a deeper investigation regarding the coupling mechanism between denitrification and anaerobic PAH degradation.