title: Microbiology and potential applications of aerobic methane oxidation coupled to denitrification (AME-D) process: A review.
abstract: Aerobic methane oxidation coupled to denitrification (AME-D) is an important link between the global methane and nitrogen cycles. This mini-review updates discoveries regarding aerobic methanotrophs and denitrifiers, as a prelude to spotlight the microbial mechanism and the potential applications of AME-D. Until recently, AME-D was thought to be accomplished by a microbial consortium where denitrifying bacteria utilize carbon intermediates, which are excreted by aerobic methanotrophs, as energy and carbon sources. Potential carbon intermediates include methanol, citrate and acetate. This mini-review presents microbial thermodynamic estimations and postulates that methanol is the ideal electron donor for denitrification, and may serve as a trophic link between methanotrophic bacteria and denitrifiers. More excitingly, new discoveries have revealed that AME-D is not only confined to the conventional synergism between methanotrophic bacteria and denitrifiers. Specifically, an obligate aerobic methanotrophic bacterium, Methylomonas denitrificans FJG1, has been demonstrated to couple partial denitrification with methane oxidation, under hypoxia conditions, releasing nitrous oxide as a terminal product. This finding not only substantially advances the understanding of AME-D mechanism, but also implies an important but unknown role of aerobic methanotrophs in global climate change through their influence on both the methane and nitrogen cycles in ecosystems. Hence, further investigation on AME-D microbiology and mechanism is essential to better understand global climate issues and to develop niche biotechnological solutions. This mini-review also presents traditional microbial techniques, such as pure cultivation and stable isotope probing, and powerful microbial techniques, such as (meta-) genomics and (meta-) transcriptomics, for deciphering linked methane oxidation and denitrification. Although AME-D has immense potential for nitrogen removal from wastewater, drinking water and groundwater, bottlenecks and potential issues are also discussed.
authors.affiliation: Institute of Environmental Science and Technology, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Institute of Environmental Science and Technology, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, China.
authors.forename: Mengdong
authors.initials: M
authors.lastname: Yuan
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
authors.forename: Giin-Yu Amy
authors.initials: GA
authors.lastname: Tan
authors.affiliation: Institute of Environmental Science and Technology, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, China.
authors.forename: Faqian
authors.initials: F
authors.lastname: Sun
authors.affiliation: Institute of Environmental Science and Technology, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Wang
authors.affiliation: Institute of Environmental Science and Technology, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, China. Electronic address: weixiang@zju.edu.cn.
authors.forename: Weixiang
authors.initials: W
authors.lastname: Wu
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
authors.forename: Po-Heng
authors.initials: PH
authors.lastname: Lee
mesh_terms: D000085:Acetates / Q000737:chemistry; D019149:Bioreactors; D002244:Carbon / Q000737:chemistry; D019343:Citric Acid / Q000737:chemistry; D058440:Denitrification; D060587:Groundwater; D008697:Methane / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D059013:Microbial Consortia; D009566:Nitrates; D009584:Nitrogen / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification*; D058458:Nitrogen Cycle; D010100:Oxygen / Q000737:chemistry; D013816:Thermodynamics; D062065:Wastewater; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods*
chemical_list: D000085:Acetates; D002244:Carbon; D019343:Citric Acid; D008697:Methane; D000432:Methanol; D009566:Nitrates; D009584:Nitrogen; D010100:Oxygen; D062065:Wastewater
keywords: Aerobic methane oxidation coupled to denitrification (AME-D); Aerobic methanotrophs; Denitrifiers; Methodology; Potential applications; Thermodynamics