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Cable bacteria play an essential role in biogeochemical processes in sediments by long-distance electron transport (LDET). A potential relationship has been found between cable bacteria and organic contaminant removal; however, the mechanisms remain unclear. In this study, the response of cable bacteria to pyrene was investigated in sediments with and without pyrene, and the effect of cable bacteria on pyrene removal was explored by connecting and blocking the paths of cable bacteria to the suboxic zones. The results showed that pyrene significantly influenced the microbial community structure and the composition of cable bacteria. The pyrene removal efficiencies significantly increased with the enrichment of cable bacteria, while sulfur-reducing microorganisms and aromatic compound degraders were also significantly enriched and correlated with cable bacteria abundance. Metagenomic analysis showed that cable bacteria have a potential LDET-bound acetate/formate respiratory pathway to gain energy. The presence of pyrene probably selects and enriches cable bacteria with a high tolerance to organic contaminants and changes the related functional microbial community, leading to the acceleration of pyrene removal. This study provides new insights into the interaction mechanisms between contaminants and cable bacteria, shedding light on the applications of cable bacteria in the bioremediation of contaminants in sediments.

A promising process is under development for the removal of NOx and regeneration of Fe(II)EDTA in a novel biotrickling filter–anaerobic baffled reactor (BTF–ABR) integrated system at 50 ± 0.5 ℃. In this work, we investigated the NOx removal capacity of a BTF under different O2 concentrations (7.0 vol%, 5.25 vol% and 3.5 vol%), and tested the effect of an ABR on NOx removal and regeneration of Fe(II)EDTA. The results showed that the NOx removal capacity was significantly increased with the O2 concentration reduced from 7.0% to 3.5%. The microoxygen environment produced by the BTF–ABR integrated system was more conducive to the removal of NOx and regeneration of Fe(II)EDTA compared with that in the BTF. Real–time polymerase chain reaction (PCR) analysis showed that the coordinated expression of denitrification genes was the major reason for no N2O emission, along with no nitrate and nitrite accumulation. The 16S rRNA gene amplicon sequencing analysis showed that the cooperation of denitrifying bacteria (Klebsiella, Petrimonas, Rhodococcus and Ochrobactium) and iron–reducing bacteria (Klebsiella, Geobacter and Petrimonas) in the system was the key to the stable and efficient removal of NOx and the regeneration of Fe(II)EDTA simultaneously.

Microbial sulfate-reduction coupling polycyclic aromatic hydrocarbon (PAH) degradation is an important process for the remediation of contaminated sediments. However, little is known about core players and their mechanisms in this process due to the complexity of PAH degradation and the large number of microorganisms involved. Here we analyzed potential core players in a black-odorous sediment using gradient-dilution culturing, isolation and genomic/metagenomic approaches. Along the dilution gradient, microbial PAH degradation and sulfate consumption were not decreased, and even a significant (p = 0.003) increase was observed in the degradation of phenanthrene although the microbial diversity declined. Two species, affiliated with Desulfovibrio and Petrimonas, were commonly present in all of the gradients as keystone taxa and showed as the dominant microorganisms in the single colony (SB8) isolated from the highest dilution culture with 93.49% and 4.73% of the microbial community, respectively. Desulfovibrio sp. SB8 and Petrimonas sp. SB8 could serve together as core players for sulfate-reduction coupling PAH degradation, in which Desulfovibrio sp. SB8 could degrade PAHs to hexahydro-2-naphthoyl through the carboxylation pathway while Petrimonas sp. SB8 might degrade intermediate metabolites of PAHs. This study provides new insights into the microbial sulfate-reduction coupling PAH degradation in black-odorous sediments.