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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 (N 2 O and N 2 ) involved in denitrification, and abundances of denitrification concerned genes ( narG :periplasmic nitrate reeducates gene; nirS : cd 1 -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 N 2 O[3.39 μg ·(L ·h) -1 ] and N 2 [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.

It has previously been confirmed that polycyclic aromatic hydrocarbons (PAHs) could be degraded by soil microbes coupling with denitrification, but the relationships among soil denitrifiers, PAHs, and nitrate under obligate anaerobic condition are still unclear. Here, co-effects of pyrene and nitrate on the activity and abundance of soil denitrifiers were investigated through a 45-day incubation experiment. Two groups of soil treatments with (N 30 ) and without (N 0 ) nitrate (30 mg kg -1 dry soil) amendment were conducted, and each group contained three treatments with different pyrene concentrations (0, 30, and 60 mg kg -1 dry soil denoted as P 0 , P 30 , and P 60 , respectively). The pyrene content, abundances of denitrification concerning genes (narG, periplasmic nitrate reductase gene; nirS, cd 1 -nitrite reductase gene; nirK, copper-containing nitrite reductase gene), and productions of N 2 O and CO 2 were measured at day 3, 14, 28, and 45, and the bacterial community structures in four represented treatments (N 0 P 0 , N 0 P 60 , N 30 P 0 , and N 30 P 60 ) were analyzed at day 45. The results indicated that the treatments with higher pyrene concentration had higher final pyrene removal rates than the treatments with lower pyrene concentration. Additionally, intensive emission of N 2 O was detected in all treatments only at day 3, but a continuous production of CO 2 was measured in each treatment during the incubation. Nitrate amendment could enhance the activity of soil denitrifiers, and be helpful for soil microbes to sustain their activity. While pyrene seemed had no influence on the productions of N 2 O and CO 2 , and amendment with pyrene or nitrate both had no obvious effect on abundances of denitrification concerning genes. Furthermore, it was nitrate but not pyrene had an obvious influence on the community structure of soil bacteria. These results revealed that, under anaerobic condition, the activity and abundance of soil denitrifiers both were insensitive to pyrene, but nitrate could improve the activity of soil denitrfiers and induce the shifts in soil bacterial community structure.

Agricultural soils in oilfields have high risk for polycyclic aromatic hydrocarbon (PAH) pollution. In this study, from the Jianghan Oilfield (Hubei Province, China) with a history of >50 years, 7 soil samples (OS-1 to OS-7) were collected. Subsequently, the bacterial, archaeal, and fungal community structures were investigated by Illumina MiSeq sequencing, and the relationship between microbial community structure and soil PAH content was analyzed. The results indicated that bacterial and archaeal Chao 1 indices showed a significantly negative relationship with soil PAH content, and only the bacterial Shannon index had a significantly negative relationship with soil PAH content. Moreover, the community structure of bacteria (r 2  = 0.9001, p = 0.013) showed a stronger correlation with PAH content than that of fungi (r 2  = 0.7357, p = 0.045), and no significant relationship was found between archaeal community structure (r 2  = 0.4553, p = 0.262) and soil PAH content. In addition, the relative greater abundances of some bacterial genus belonging to Actinobacteria (Mycobacterium and Micromonospora) and Proteobacteria (Pseudomonas, Lysobacter, Idiomarina, Oxalobacteraceae, and Massilia), fungal genus belonging to Ascomycota (Sordariales and Pleosporales), and archaeal phylum (Euryarchaeota) were detected in the soil samples (OS-3 and OS-5) with greater PAH content. In summary, soil PAHs showed an obvious influence and selectivity on the soil microbiota. Furthermore, compared with fungi and archaea, bacteria was more sensitive to soil PAH pollution, and the diversity indices and community structure of bacteria both might be suitable indicators for assessment of soil PAH stress on the soil ecosystem.