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Reis PCJ, Tsuji JM, Weiblen C, Schiff SL, Scott M, Stein LY, Neufeld JD. Enigmatic persistence of aerobic methanotrophs in oxygen-limiting freshwater habitats. THE ISME JOURNAL 2024; 18:wrae041. [PMID: 38470309 PMCID: PMC11008690 DOI: 10.1093/ismejo/wrae041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Revised: 01/06/2024] [Accepted: 03/13/2024] [Indexed: 03/13/2024]
Abstract
Methanotrophic bacteria mitigate emissions of the potent greenhouse gas methane (CH4) from a variety of anthropogenic and natural sources, including freshwater lakes, which are large sources of CH4 on a global scale. Despite a dependence on dioxygen (O2) for CH4 oxidation, abundant populations of putatively aerobic methanotrophs have been detected within microoxic and anoxic waters and sediments of lakes. Experimental work has demonstrated active aerobic methanotrophs under those conditions, but how they are able to persist and oxidize CH4 under O2 deficiency remains enigmatic. In this review, we discuss possible mechanisms that underpin the persistence and activity of aerobic methanotrophs under O2-limiting conditions in freshwater habitats, particularly lakes, summarize experimental evidence for microbial oxidation of CH4 by aerobic bacteria under low or no O2, and suggest future research directions to further explore the ecology and metabolism of aerobic methanotrophs in O2-limiting environments.
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Affiliation(s)
- Paula C J Reis
- Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Jackson M Tsuji
- Super-cutting-edge Grand and Advanced Research (SUGAR) Program, Institute for Extra-cutting-edge Science and Technology Avant-garde Research, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa, Japan
| | - Cerrise Weiblen
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Sherry L Schiff
- Department of Earth & Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Matthew Scott
- Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Lisa Y Stein
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Josh D Neufeld
- Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada
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Beals DG, Puri AW. Linking methanotroph phenotypes to genotypes using a simple spatially resolved model ecosystem. THE ISME JOURNAL 2024; 18:wrae060. [PMID: 38622932 PMCID: PMC11072679 DOI: 10.1093/ismejo/wrae060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 02/20/2024] [Accepted: 04/10/2024] [Indexed: 04/17/2024]
Abstract
Connecting genes to phenotypic traits in bacteria is often challenging because of a lack of environmental context in laboratory settings. Laboratory-based model ecosystems offer a means to better account for environmental conditions compared with standard planktonic cultures and can help link genotypes and phenotypes. Here, we present a simple, cost-effective, laboratory-based model ecosystem to study aerobic methane-oxidizing bacteria (methanotrophs) within the methane-oxygen counter gradient typically found in the natural environment of these organisms. Culturing the methanotroph Methylomonas sp. strain LW13 in this system resulted in the formation of a distinct horizontal band at the intersection of the counter gradient, which we discovered was not due to increased numbers of bacteria at this location but instead to an increased amount of polysaccharides. We also discovered that different methanotrophic taxa form polysaccharide bands with distinct locations and morphologies when grown in the methane-oxygen counter gradient. By comparing transcriptomic data from LW13 growing within and surrounding this band, we identified genes upregulated within the band and validated their involvement in growth and band formation within the model ecosystem using knockout strains. Notably, deletion of these genes did not negatively affect growth using standard planktonic culturing methods. This work highlights the use of a laboratory-based model ecosystem that more closely mimics the natural environment to uncover bacterial phenotypes missing from standard laboratory conditions, and to link these phenotypes with their genetic determinants.
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Affiliation(s)
- Delaney G Beals
- Department of Chemistry and the Henry Eyring Center for Cell and Genome Science, University of Utah, Salt Lake City, UT 84112, United States
| | - Aaron W Puri
- Department of Chemistry and the Henry Eyring Center for Cell and Genome Science, University of Utah, Salt Lake City, UT 84112, United States
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Wang Y, Wu M, Lai CY, Lu X, Guo J. Methane Oxidation Coupled to Selenate Reduction in a Membrane Bioreactor under Oxygen-Limiting Conditions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:21715-21726. [PMID: 38079577 DOI: 10.1021/acs.est.3c04958] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2023]
Abstract
Microbial methane oxidation coupled to a selenate reduction process has been proposed as a promising solution to treat contaminated water, yet the underlying microbial mechanisms are still unclear. In this study, a novel methane-based membrane bioreactor system integrating hollow fiber membranes for efficient gas delivery and ultrafiltration membranes for biomass retention was established to successfully enrich abundant suspended cultures able to perform methane-dependent selenate reduction under oxygen-limiting conditions. The microbial metabolic mechanisms were then systematically investigated through a combination of short-term batch tests, DNA-based stable isotope probing (SIP) microcosm incubation, and high-throughput sequencing analyses of 16S rRNA gene and functional genes (pmoA and narG). We confirmed that the methane-supported selenate reduction process was accomplished by a microbial consortia consisting of type-II aerobic methanotrophs and several heterotrophic selenate reducers. The mass balance and validation tests on possible intermediates suggested that methane was partially oxidized into acetate under oxygen-limiting conditions, which was consumed as a carbon source for selenate-reducing bacteria. High-throughput 16S rRNA gene sequencing, DNA-SIP incubation with 13CH4, and subsequent functional gene (pmoA and narG) sequencing results collectively proved that Methylocystis actively executed partial methane oxidation and Acidovorax and Denitratisoma were dominant selenate-reducing bacteria, thus forming a syntrophic partnership to drive selenate reduction. The findings not only advance our understanding of methane oxidation coupled to selenate reduction under oxygen-limiting conditions but also offer useful information on developing methane-based biotechnology for bioremediation of selenate-contaminated water.
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Affiliation(s)
- Yulu Wang
- Australian Centre for Water and Environmental Biotechnology (ACWEB, Formerly AWMC), The University of Queensland, St Lucia, Queensland 4072, Australia
- Commonwealth Scientific and Industrial Research Organisation (CSIRO), Acton, Canberra, Australian Capital Territory 2601, Australia
| | - Mengxiong Wu
- Australian Centre for Water and Environmental Biotechnology (ACWEB, Formerly AWMC), The University of Queensland, St Lucia, Queensland 4072, Australia
| | - Chun-Yu Lai
- Australian Centre for Water and Environmental Biotechnology (ACWEB, Formerly AWMC), The University of Queensland, St Lucia, Queensland 4072, Australia
| | - Xuanyu Lu
- Australian Centre for Water and Environmental Biotechnology (ACWEB, Formerly AWMC), The University of Queensland, St Lucia, Queensland 4072, Australia
| | - Jianhua Guo
- Australian Centre for Water and Environmental Biotechnology (ACWEB, Formerly AWMC), The University of Queensland, St Lucia, Queensland 4072, Australia
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Guerrero-Cruz S, Vaksmaa A, Horn MA, Niemann H, Pijuan M, Ho A. Methanotrophs: Discoveries, Environmental Relevance, and a Perspective on Current and Future Applications. Front Microbiol 2021; 12:678057. [PMID: 34054786 PMCID: PMC8163242 DOI: 10.3389/fmicb.2021.678057] [Citation(s) in RCA: 49] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 04/12/2021] [Indexed: 11/13/2022] Open
Abstract
Methane is the final product of the anaerobic decomposition of organic matter. The conversion of organic matter to methane (methanogenesis) as a mechanism for energy conservation is exclusively attributed to the archaeal domain. Methane is oxidized by methanotrophic microorganisms using oxygen or alternative terminal electron acceptors. Aerobic methanotrophic bacteria belong to the phyla Proteobacteria and Verrucomicrobia, while anaerobic methane oxidation is also mediated by more recently discovered anaerobic methanotrophs with representatives in both the bacteria and the archaea domains. The anaerobic oxidation of methane is coupled to the reduction of nitrate, nitrite, iron, manganese, sulfate, and organic electron acceptors (e.g., humic substances) as terminal electron acceptors. This review highlights the relevance of methanotrophy in natural and anthropogenically influenced ecosystems, emphasizing the environmental conditions, distribution, function, co-existence, interactions, and the availability of electron acceptors that likely play a key role in regulating their function. A systematic overview of key aspects of ecology, physiology, metabolism, and genomics is crucial to understand the contribution of methanotrophs in the mitigation of methane efflux to the atmosphere. We give significance to the processes under microaerophilic and anaerobic conditions for both aerobic and anaerobic methane oxidizers. In the context of anthropogenically influenced ecosystems, we emphasize the current and potential future applications of methanotrophs from two different angles, namely methane mitigation in wastewater treatment through the application of anaerobic methanotrophs, and the biotechnological applications of aerobic methanotrophs in resource recovery from methane waste streams. Finally, we identify knowledge gaps that may lead to opportunities to harness further the biotechnological benefits of methanotrophs in methane mitigation and for the production of valuable bioproducts enabling a bio-based and circular economy.
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Affiliation(s)
- Simon Guerrero-Cruz
- Catalan Institute for Water Research (ICRA), Girona, Spain
- Universitat de Girona, Girona, Spain
| | - Annika Vaksmaa
- Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, ’t Horntje, Netherlands
| | - Marcus A. Horn
- Institute of Microbiology, Leibniz Universität Hannover, Hannover, Germany
| | - Helge Niemann
- Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, ’t Horntje, Netherlands
- Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, Netherlands
- Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT the Arctic University of Norway, Tromsø, Norway
| | - Maite Pijuan
- Catalan Institute for Water Research (ICRA), Girona, Spain
- Universitat de Girona, Girona, Spain
| | - Adrian Ho
- Institute of Microbiology, Leibniz Universität Hannover, Hannover, Germany
- Division of Applied Life Sciences, Gyeongsang National University, Jinju, South Korea
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Nariya S, Kalyuzhnaya MG. Hemerythrins enhance aerobic respiration in Methylomicrobium alcaliphilum 20ZR, a methane-consuming bacterium. FEMS Microbiol Lett 2020; 367:5735436. [PMID: 32053143 DOI: 10.1093/femsle/fnaa003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Accepted: 02/03/2020] [Indexed: 01/04/2023] Open
Abstract
Numerous hemerythrins, di-iron proteins, have been identified in prokaryote genomes, but in most cases their function remains elusive. Bacterial hemerythrin homologs (bacteriohemerythrins, Bhrs) may contribute to various cellular functions, including oxygen sensing, metal binding and antibiotic resistance. It has been proposed that methanotrophic Bhrs support methane oxidation by supplying oxygen to a core enzyme, particulate methane monooxygenase. In this study, the consequences of the overexpression or deletion of the Bhr gene (bhr) in Methylomicrobiam alcaliphillum 20ZR were investigated. We found that the bhrknockout (20ZRΔbhr) displays growth kinetics and methane consumption rates similar to wild type. However, the 20ZRΔbhr accumulates elevated concentrations of acetate at aerobic conditions, indicating slowed respiration. The methanotrophic strain overproducing Bhr shows increased oxygen consumption and reduced carbon-conversion efficiency, while its methane consumption rates remain unchanged. These results suggest that the methanotrophic Bhr proteins specifically contribute to oxygen-dependent respiration, while they have minimal, if any, input of oxygen for the methane oxidation machinery.
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Affiliation(s)
- Snehal Nariya
- Biology Department, 5500 Campanile Drive, San Diego, CA, USA
| | - Marina G Kalyuzhnaya
- Biology Department, 5500 Campanile Drive, San Diego, CA, USA.,Viral Information Institute, San Diego State University, 5500 Campanile Drive, San Diego, CA
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Rahalkar MC, Khatri K, Pandit PS, Dhakephalkar PK. A putative novel Methylobacter member (KRF1) from the globally important Methylobacter clade 2: cultivation and salient draft genome features. Antonie van Leeuwenhoek 2019; 112:1399-1408. [PMID: 30968234 DOI: 10.1007/s10482-019-01262-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Accepted: 04/02/2019] [Indexed: 11/28/2022]
Abstract
Methane oxidation by methanotrophs is a very important environmental process in the mitigation of methane. Methylobacter (Mtb.) clade 2 members have been reported as dominant methane oxidisers in soils and sediments worldwide. We enriched and purified a methanotroph from a tropical rice field soil sample from India. The highly enriched culture showed the presence of motile, long and thick rods (3-5 µm × 0.9-1.2 µm) and minor presence of short, thin rods. The culture was purified on agarose medium and formed yellow colonies which showed the presence of only thick and long rods, henceforth termed as strain KRF1. Based on 16S rRNA gene sequence analysis, strain KRF1 shows close phylogenetic affiliation to Methylobacter tundripaludum SV96T (98.6% similarity). Due to the taxonomic novelty, and being the first member of Mtb. related to Mtb. tundripaludum from the tropics, the draft genome was sequenced. From the blastx analysis of the contigs, it was clear that the culture still had contamination of another organism, a Methylophilus species. The data binned in two clear bins: Mtb. related contigs and Methylophilus-related contigs. The binned draft genome of KRF1 shows features including the typical pathways for methane metabolism, denitrification and the presence of molybdenum iron and vanadium-iron nitrogenase genes. KRF1 is phylogenetically distinct from the five strains of Mtb. tundripaludum including SV96T, Lake Washington strains and OWC strains, showing ~ 26% DDH and ~ 81% ANIb values and a unique position in a phylogenomic tree. Subsequently, KRF1 has been completely purified from its methylotrophic partner and a pure culture has been established and maintained in a WDCM approved culture collection, the MACS Collection of Microorganisms (as MCM 1471). KRF1 is thus the first cultured member of a putative novel species of Methylobacter clade 2 isolated from the tropics.
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Affiliation(s)
- Monali C Rahalkar
- C2, Bioenergy Group, MACS Agharkar Research Institute, G.G. Agarkar Road, Pune, Maharashtra, 411004, India. .,Savitribai Phule Pune University, Ganeshkhind Road, Pune, Maharashtra, 411007, India.
| | - Kumal Khatri
- C2, Bioenergy Group, MACS Agharkar Research Institute, G.G. Agarkar Road, Pune, Maharashtra, 411004, India.,Savitribai Phule Pune University, Ganeshkhind Road, Pune, Maharashtra, 411007, India
| | - Pranitha S Pandit
- C2, Bioenergy Group, MACS Agharkar Research Institute, G.G. Agarkar Road, Pune, Maharashtra, 411004, India.,Savitribai Phule Pune University, Ganeshkhind Road, Pune, Maharashtra, 411007, India
| | - Prashant K Dhakephalkar
- C2, Bioenergy Group, MACS Agharkar Research Institute, G.G. Agarkar Road, Pune, Maharashtra, 411004, India.,Savitribai Phule Pune University, Ganeshkhind Road, Pune, Maharashtra, 411007, India
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Description of ‘Candidatus Methylocucumis oryzae’, a novel Type I methanotroph with large cells and pale pink colour, isolated from an Indian rice field. Antonie van Leeuwenhoek 2018; 111:2473-2484. [DOI: 10.1007/s10482-018-1136-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Accepted: 07/26/2018] [Indexed: 11/25/2022]
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