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The environmental problem posed by shale gas wastewater has received considerable research attention. Researchers mostly focus on the technical aspect of terminal centralized treatment with little concern on the topic of early collection and on-site pretreatment of PW near gas gathering stations. In this study, the short-term fluctuations of the DOM molecular composition and the concurrent transformation of the microbial community and functions were carefully examined when the PW was temporarily stored in a simulated reservoir near gas wells. Ultra-high resolution mass spectrometry was used to determine the molecular structure of the DOM samples. The data showed that during the short-term storage of PW, strongly polarized and nonvolatile organic compounds developed a complex molecular structure, resulting in molecules that were more unsaturated and lower bioavailability. Microbial activity was responsible for the changes in organic matter composition that occurred in the later stages of the storage process, during which the amount of nitrogenous organic molecules increased. Network analysis offered vital information on microbial functions related to organic matter composition and the patterns of interaction between them. Organic molecule consumption and accumulation were intimately connected to the interactions between various bacteria the same as the consumption and accumulation of DOM molecules. [ABSTRACT FROM AUTHOR]

• A stable hypoxic AME-D process was established in a methane-cycling bioreactor. • Genome-centric metagenomics with DNA-SIP were used to assess metabolic mechanism. • Methylomonas were actively prevalent at the enriched hypoxic AME-D community. • A new genome of Methylococcaceae with abundant denitrification genes was obtained. • Aerobic methanotrophs can accomplish partial denitrification independently. Obligate aerobic methanotrophs have been proven to oxidize methane and participate in denitrification under hypoxic conditions. However, this phenomenon and its metabolic mechanism have not been investigated in detail in aerobic methane oxidation coupled to denitrification (AME-D) process. In this study, a type of hypoxic AME-D consortium was enriched and operated for a long time in a CH 4 -cycling bioreactor with strict anaerobic control and the nitrite removal rate reached approximately 50 mg N/L/d. Metagenomics combined with DNA stable-isotope probing demonstrated that the genus Methylomonas , which constitutes type I aerobic methanotrophs, was the dominant member and contributed to methane oxidation and partial denitrification. Metagenomic binning recovered a near-complete (98%) draft genome affiliated with the family Methylococcaceae containing essential genes that encode nitrite reductase (nirK), nitric oxide reductase (norBC) and hydroxylamine dehydrogenase (hao). Metabolic reconstruction of the selected Methylococcaceae genomes also revealed a potential link between methanotrophy and partial denitrification. [ABSTRACT FROM AUTHOR]