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Li B, Mao Z, Xue J, Xing P, Wu QL. Metabolic versatility of aerobic methane-oxidizing bacteria under anoxia in aquatic ecosystems. ENVIRONMENTAL MICROBIOLOGY REPORTS 2024; 16:e70002. [PMID: 39232853 PMCID: PMC11374530 DOI: 10.1111/1758-2229.70002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Accepted: 07/26/2024] [Indexed: 09/06/2024]
Abstract
The potential positive feedback between global aquatic deoxygenation and methane (CH4) emission emphasizes the importance of understanding CH4 cycling under O2-limited conditions. Increasing observations for aerobic CH4-oxidizing bacteria (MOB) under anoxia have updated the prevailing paradigm that MOB are O2-dependent; thus, clarification on the metabolic mechanisms of MOB under anoxia is critical and timely. Here, we mapped the global distribution of MOB under anoxic aquatic zones and summarized four underlying metabolic strategies for MOB under anoxia: (a) forming a consortium with oxygenic microorganisms; (b) self-generation/storage of O2 by MOB; (c) forming a consortium with non-oxygenic heterotrophic bacteria that use other electron acceptors; and (d) utilizing alternative electron acceptors other than O2. Finally, we proposed directions for future research. This study calls for improved understanding of MOB under anoxia, and underscores the importance of this overlooked CH4 sink amidst global aquatic deoxygenation.
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Affiliation(s)
- Biao Li
- Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
| | - Zhendu Mao
- Center for Evolution and Conservation Biology, Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China
| | - Jingya Xue
- School of Geographical Sciences, Nanjing Normal University, Nanjing, China
| | - Peng Xing
- Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
| | - Qinglong L Wu
- Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
- Center for Evolution and Conservation Biology, Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China
- Sino-Danish Center for Education and Research, University of Chinese Academy of Sciences, Beijing, China
- The Fuxianhu Station of Plateau Deep Lake Research, Chinese Academy of Sciences, Yuxi, China
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Peng P, DiSpirito AA, Lewis BJ, Nott JD, Semrau JD. Heterologous Biosynthesis of Methanobactin from Methylocystis sp. Strain SB2 in Methylosinus trichosporium OB3b. ACS Synth Biol 2024; 13:2347-2356. [PMID: 39109930 DOI: 10.1021/acssynbio.4c00026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/17/2024]
Abstract
Aerobic methanotrophs, or methane-consuming microbes, are strongly dependent on copper for their activity. To satisfy this requirement, some methanotrophs produce a copper-binding compound, or chalkophore, called methanobactin (MB). In addition to playing a critical role in methanotrophy, MB has also been shown to have great promise in treating copper-related human diseases, perhaps most significantly Wilson's disease. In this congenital disorder, copper builds up in the liver, leading to irreversible damage and, in severe cases, complete organ failure. Remarkably, MB has been shown to reverse such damage in animal models, and there is a great deal of interest in upscaling MB production for expanded clinical trials. Such efforts, however, are currently hampered as (1) the natural rate of MB production rate by methanotrophs is low, (2) the use of methane as a substrate for MB production is problematic as it is explosive in air, (3) there is limited understanding of the entire pathway of MB biosynthesis, and (4) the most attractive form of MB is produced by Methylocystis sp. strain SB2, a methanotroph that is genetically intractable. Herein, we report heterologous biosynthesis of MB from Methylocystis sp. strain SB2 in an alternative methanotroph, Methylosinus trichosporium OB3b, not only on methane but also on methanol. As a result, the strategy described herein not only facilitates enhanced MB production but also provides opportunities to construct various mutants to delineate the entire pathway of MB biosynthesis, as well as the creation of modified forms of MB that may have enhanced therapeutic value.
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Affiliation(s)
- Peng Peng
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan 48109-2125, United States
| | - Alan A DiSpirito
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011-3260, United States
| | - Braden J Lewis
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011-3260, United States
| | - Joel D Nott
- Office of Biotechnology Protein Facility, Iowa State University, Ames, Iowa 50011-3260, United States
| | - Jeremy D Semrau
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan 48109-2125, United States
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Almog G, Rubin-Blum M, Murrell C, Vigderovich H, Eckert W, Larke-Mejía N, Sivan O. Survival strategies of aerobic methanotrophs under hypoxia in methanogenic lake sediments. ENVIRONMENTAL MICROBIOME 2024; 19:44. [PMID: 38956741 PMCID: PMC11218250 DOI: 10.1186/s40793-024-00586-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Accepted: 06/23/2024] [Indexed: 07/04/2024]
Abstract
BACKGROUND Microbial methane oxidation, methanotrophy, plays a crucial role in mitigating the release of the potent greenhouse gas methane from aquatic systems. While aerobic methanotrophy is a well-established process in oxygen-rich environments, emerging evidence suggests their activity in hypoxic conditions. However, the adaptability of these methanotrophs to such environments has remained poorly understood. Here, we explored the genetic adaptability of aerobic methanotrophs to hypoxia in the methanogenic sediments of Lake Kinneret (LK). These LK methanogenic sediments, situated below the oxidic and sulfidic zones, were previously characterized by methane oxidation coupled with iron reduction via the involvement of aerobic methanotrophs. RESULTS In order to explore the adaptation of the methanotrophs to hypoxia, we conducted two experiments using LK sediments as inoculum: (i) an aerobic "classical" methanotrophic enrichment with ambient air employing DNA stable isotope probing (DNA-SIP) and (ii) hypoxic methanotrophic enrichment with repeated spiking of 1% oxygen. Analysis of 16S rRNA gene amplicons revealed the enrichment of Methylococcales methanotrophs, being up to a third of the enriched community. Methylobacter, Methylogaea, and Methylomonas were prominent in the aerobic experiment, while hypoxic conditions enriched primarily Methylomonas. Using metagenomics sequencing of DNA extracted from these experiments, we curated five Methylococcales metagenome-assembled genomes (MAGs) and evaluated the genetic basis for their survival in hypoxic environments. A comparative analysis with an additional 62 Methylococcales genomes from various environments highlighted several core genetic adaptations to hypoxia found in most examined Methylococcales genomes, including high-affinity cytochrome oxidases, oxygen-binding proteins, fermentation-based methane oxidation, motility, and glycogen use. We also found that some Methylococcales, including LK Methylococcales, may denitrify, while metals and humic substances may also serve as electron acceptors alternative to oxygen. Outer membrane multi-heme cytochromes and riboflavin were identified as potential mediators for the utilization of metals and humic material. These diverse mechanisms suggest the ability of methanotrophs to thrive in ecological niches previously thought inhospitable for their growth. CONCLUSIONS Our study sheds light on the ability of enriched Methylococcales methanotrophs from methanogenic LK sediments to survive under hypoxia. Genomic analysis revealed a spectrum of genetic capabilities, potentially enabling these methanotrophs to function. The identified mechanisms, such as those enabling the use of alternative electron acceptors, expand our understanding of methanotroph resilience in diverse ecological settings. These findings contribute to the broader knowledge of microbial methane oxidation and have implications for understanding and potential contribution methanotrophs may have in mitigating methane emissions in various environmental conditions.
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Affiliation(s)
- Gafni Almog
- Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel.
| | - Maxim Rubin-Blum
- Israel Limnology and Oceanography Research, Tel Shikmona, Haifa, Israel
| | - Colin Murrell
- School of Environmental Sciences, University of East Anglia, Norwich, UK
| | - Hanni Vigderovich
- Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
| | - Werner Eckert
- The Yigal Allon Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, Migdal, Israel
| | | | - Orit Sivan
- Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
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Schorn S, Graf JS, Littmann S, Hach PF, Lavik G, Speth DR, Schubert CJ, Kuypers MMM, Milucka J. Persistent activity of aerobic methane-oxidizing bacteria in anoxic lake waters due to metabolic versatility. Nat Commun 2024; 15:5293. [PMID: 38906896 PMCID: PMC11192741 DOI: 10.1038/s41467-024-49602-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Accepted: 06/07/2024] [Indexed: 06/23/2024] Open
Abstract
Lacustrine methane emissions are strongly mitigated by aerobic methane-oxidizing bacteria (MOB) that are typically most active at the oxic-anoxic interface. Although oxygen is required by the MOB for the first step of methane oxidation, their occurrence in anoxic lake waters has raised the possibility that they are capable of oxidizing methane further anaerobically. Here, we investigate the activity and growth of MOB in Lake Zug, a permanently stratified freshwater lake. The rates of anaerobic methane oxidation in the anoxic hypolimnion reached up to 0.2 µM d-1. Single-cell nanoSIMS measurements, together with metagenomic and metatranscriptomic analyses, linked the measured rates to MOB of the order Methylococcales. Interestingly, their methane assimilation activity was similar under hypoxic and anoxic conditions. Our data suggest that these MOB use fermentation-based methanotrophy as well as denitrification under anoxic conditions, thus offering an explanation for their widespread presence in anoxic habitats such as stratified water columns. Thus, the methane sink capacity of anoxic basins may have been underestimated by not accounting for the anaerobic MOB activity.
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Affiliation(s)
- Sina Schorn
- Max Planck Institute for Marine Microbiology, Bremen, Germany.
- Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
| | - Jon S Graf
- Max Planck Institute for Marine Microbiology, Bremen, Germany
| | - Sten Littmann
- Max Planck Institute for Marine Microbiology, Bremen, Germany
| | - Philipp F Hach
- Max Planck Institute for Marine Microbiology, Bremen, Germany
| | - Gaute Lavik
- Max Planck Institute for Marine Microbiology, Bremen, Germany
| | - Daan R Speth
- Max Planck Institute for Marine Microbiology, Bremen, Germany
- Division of Microbial Ecology, Center for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria
| | - Carsten J Schubert
- Department of Surface Waters, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Kastanienbaum, Switzerland
- Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, Switzerland
| | | | - Jana Milucka
- Max Planck Institute for Marine Microbiology, Bremen, Germany
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5
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Yu L, Jia R, Liu S, Li S, Zhong S, Liu G, Zeng RJ, Rensing C, Zhou S. Ferrihydrite-mediated methanotrophic nitrogen fixation in paddy soil under hypoxia. ISME COMMUNICATIONS 2024; 4:ycae030. [PMID: 38524761 PMCID: PMC10960957 DOI: 10.1093/ismeco/ycae030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Revised: 02/21/2024] [Accepted: 02/29/2024] [Indexed: 03/26/2024]
Abstract
Biological nitrogen fixation (BNF) by methanotrophic bacteria has been shown to play an important role in maintaining fertility. However, this process is still limited to aerobic methane oxidation with sufficient oxygen. It has remained unknown whether and how methanotrophic BNF proceeds in hypoxic environments. Herein, we incubated paddy soils with a ferrihydrite-containing mineral salt medium to enrich methanotrophic bacteria in the presence of methane (20%, v/v) under oxygen constraints (0.27%, v/v). The resulting microcosms showed that ferrihydrite-dependent aerobic methane oxidation significantly contributed (81%) to total BNF, increasing the 15N fixation rate by 13-fold from 0.02 to 0.28 μmol 15N2 (g dry weight soil) -1 d-1. BNF was reduced by 97% when ferrihydrite was omitted, demonstrating the involvement of ferrihydrite in methanotrophic BNF. DNA stable-isotope probing indicated that Methylocystis, Methylophilaceae, and Methylomicrobium were the dominant methanotrophs/methylotrophs that assimilated labeled isotopes (13C or 15N) into biomass. Metagenomic binning combined with electrochemical analysis suggested that Methylocystis and Methylophilaceae had the potential to perform methane-induced BNF and likely utilized riboflavin and c-type cytochromes as electron carriers for ferrihydrite reduction. It was concluded that ferrihydrite mediated methanotrophic BNF by methanotrophs/methylotrophs solely or in conjunction with iron-reducing bacteria. Overall, this study revealed a previously overlooked yet pronounced coupling of iron-dependent aerobic methane oxidation to BNF and improves our understanding of methanotrophic BNF in hypoxic zones.
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Affiliation(s)
- Linpeng Yu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Rong Jia
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
- Key Laboratory of Land Resources Evaluation and Monitoring in Southwest China, Ministry of Education, Sichuan Normal University, Chengdu, Sichuan Province 610066, China
| | - Shiqi Liu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Shuan Li
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Sining Zhong
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Guohong Liu
- Agricultural Bio-resources Research Institute, Fujian Academy of Agricultural Sciences, Fuzhou 350003, China
| | - Raymond Jianxiong Zeng
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Christopher Rensing
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Shungui Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
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6
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Vigderovich H, Eckert W, Elvert M, Gafni A, Rubin-Blum M, Bergman O, Sivan O. Aerobic methanotrophy increases the net iron reduction in methanogenic lake sediments. Front Microbiol 2023; 14:1206414. [PMID: 37577416 PMCID: PMC10415106 DOI: 10.3389/fmicb.2023.1206414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2023] [Accepted: 07/10/2023] [Indexed: 08/15/2023] Open
Abstract
In methane (CH4) generating sediments, methane oxidation coupled with iron reduction was suggested to be catalyzed by archaea and bacterial methanotrophs of the order Methylococcales. However, the co-existence of these aerobic and anaerobic microbes, the link between the processes, and the oxygen requirement for the bacterial methanotrophs have remained unclear. Here, we show how stimulation of aerobic methane oxidation at an energetically low experimental environment influences net iron reduction, accompanied by distinct microbial community changes and lipid biomarker patterns. We performed incubation experiments (between 30 and 120 days long) with methane generating lake sediments amended with 13C-labeled methane, following the additions of hematite and different oxygen levels in nitrogen headspace, and monitored methane turnover by 13C-DIC measurements. Increasing oxygen exposure (up to 1%) promoted aerobic methanotrophy, considerable net iron reduction, and the increase of microbes, such as Methylomonas, Geobacter, and Desulfuromonas, with the latter two being likely candidates for iron recycling. Amendments of 13C-labeled methanol as a potential substrate for the methanotrophs under hypoxia instead of methane indicate that this substrate primarily fuels methylotrophic methanogenesis, identified by high methane concentrations, strongly positive δ13CDIC values, and archaeal lipid stable isotope data. In contrast, the inhibition of methanogenesis by 2-bromoethanesulfonate (BES) led to increased methanol turnover, as suggested by similar 13C enrichment in DIC and high amounts of newly produced bacterial fatty acids, probably derived from heterotrophic bacteria. Our experiments show a complex link between aerobic methanotrophy and iron reduction, which indicates iron recycling as a survival mechanism for microbes under hypoxia.
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Affiliation(s)
- Hanni Vigderovich
- Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
| | - Werner Eckert
- The Yigal Allon Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, Migdal, Israel
| | - Marcus Elvert
- MARUM—Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen, Bremen, Germany
| | - Almog Gafni
- Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
| | - Maxim Rubin-Blum
- Israel Oceanographic and Limnological Research, National Institute of Oceanography, Haifa, Israel
| | - Oded Bergman
- Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
- The Yigal Allon Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, Migdal, Israel
| | - Orit Sivan
- Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
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7
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Li B, Tao Y, Mao Z, Gu Q, Han Y, Hu B, Wang H, Lai A, Xing P, Wu QL. Iron oxides act as an alternative electron acceptor for aerobic methanotrophs in anoxic lake sediments. WATER RESEARCH 2023; 234:119833. [PMID: 36889095 DOI: 10.1016/j.watres.2023.119833] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2022] [Revised: 02/13/2023] [Accepted: 03/02/2023] [Indexed: 06/18/2023]
Abstract
Conventional aerobic CH4-oxidizing bacteria (MOB) are frequently detected in anoxic environments, but their survival strategy and ecological contribution are still enigmatic. Here we explore the role of MOB in enrichment cultures under O2 gradients and an iron-rich lake sediment in situ by combining microbiological and geochemical techniques. We found that enriched MOB consortium used ferric oxides as alternative electron acceptors for oxidizing CH4 with the help of riboflavin when O2 was unavailable. Within the MOB consortium, MOB transformed CH4 to low molecular weight organic matter such as acetate for consortium bacteria as a carbon source, while the latter secrete riboflavin to facilitate extracellular electron transfer (EET). Iron reduction coupled to CH4 oxidation mediated by the MOB consortium was also demonstrated in situ, reducing 40.3% of the CH4 emission in the studied lake sediment. Our study indicates how MOBs survive under anoxia and expands the knowledge of this previously overlooked CH4 sink in iron-rich sediments.
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Affiliation(s)
- Biao Li
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
| | - Ye Tao
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100039, China
| | - Zhendu Mao
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100039, China
| | - Qiujin Gu
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, Nanjing 210023, China
| | - Yixuan Han
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100039, China
| | - Baolan Hu
- Department of Environmental Engineering, Zhejiang University, Hangzhou 310058, China
| | - Hongwei Wang
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100039, China
| | - Anxing Lai
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100039, China
| | - Peng Xing
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
| | - Qinglong L Wu
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; Sino-Danish Centre for Education and Research, University of Chinese Academy of Sciences, Beijing 100039, China; Center for Evolution and Conservation Biology, Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China.
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Evidence for methanobactin "Theft" and novel chalkophore production in methanotrophs: impact on methanotrophic-mediated methylmercury degradation. THE ISME JOURNAL 2022; 16:211-220. [PMID: 34290379 PMCID: PMC8692452 DOI: 10.1038/s41396-021-01062-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Revised: 07/02/2021] [Accepted: 07/08/2021] [Indexed: 02/07/2023]
Abstract
Aerobic methanotrophy is strongly controlled by copper, and methanotrophs are known to use different mechanisms for copper uptake. Some methanotrophs secrete a modified polypeptide-methanobactin-while others utilize a surface-bound protein (MopE) and a secreted form of it (MopE*) for copper collection. As different methanotrophs have different means of sequestering copper, competition for copper significantly impacts methanotrophic activity. Herein, we show that Methylomicrobium album BG8, Methylocystis sp. strain Rockwell, and Methylococcus capsulatus Bath, all lacking genes for methanobactin biosynthesis, are not limited for copper by multiple forms of methanobactin. Interestingly, Mm. album BG8 and Methylocystis sp. strain Rockwell were found to have genes similar to mbnT that encodes for a TonB-dependent transporter required for methanobactin uptake. Data indicate that these methanotrophs "steal" methanobactin and such "theft" enhances the ability of these strains to degrade methylmercury, a potent neurotoxin. Further, when mbnT was deleted in Mm. album BG8, methylmercury degradation in the presence of methanobactin was indistinguishable from when MB was not added. Mc. capsulatus Bath lacks anything similar to mbnT and was unable to degrade methylmercury either in the presence or absence of methanobactin. Rather, Mc. capsulatus Bath appears to rely on MopE/MopE* for copper collection. Finally, not only does Mm. album BG8 steal methanobactin, it synthesizes a novel chalkophore, suggesting that some methanotrophs utilize both competition and cheating strategies for copper collection. Through a better understanding of these strategies, methanotrophic communities may be more effectively manipulated to reduce methane emissions and also enhance mercury detoxification in situ.
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Adapting Macroecology to Microbiology: Using Occupancy Modeling To Assess Functional Profiles across Metagenomes. mSystems 2021; 6:e0079021. [PMID: 34874772 PMCID: PMC8651082 DOI: 10.1128/msystems.00790-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Metagenomic sequencing provides information on the metabolic capacities and taxonomic affiliations for members of a microbial community. When assessing metabolic functions in a community, missing genes in pathways can occur in two ways; the genes may legitimately be missing from the community whose DNA was sequenced, or the genes were missed during shotgun sequencing or failed to assemble, and thus the metabolic capacity of interest is wrongly absent from the sequence data. Here, we borrow and adapt occupancy modeling from macroecology to provide mathematical context to metabolic predictions from metagenomes. We review the five assumptions underlying occupancy modeling through the lens of microbial community sequence data. Using the methane cycle, we apply occupancy modeling to examine the presence and absence of methanogenesis and methanotrophy genes from nearly 10,000 metagenomes spanning global environments. We determine that methanogenesis and methanotrophy are positively correlated across environments, providing a predictive framework for assessing gene absences for these functions. We present this adaptation of macroecology’s occupancy modeling to metagenomics as a tool to quantify the uncertainty in predictions of the presence/absence of traits in environmental microbiological surveys. We further initiate a call for stronger metadata standards to accompany metagenome deposition, to enable robust statistical approaches in the future. IMPORTANCE Metagenomics is maturing rapidly as a field but is hampered by a lack of available statistical tools. A primary area of uncertainty is around missing genes or functions from a metagenomic data set. Here, we borrow an established modeling approach from macroecology and adapt it to metagenomic data sets. Rather than multiple sampling trips to a specific area to detect a species of interest (e.g., identifying a cardinal in a forest), we leverage the enormous amount of information within a metagenome and use multiple gene markers for a function of interest (e.g., subunits of an enzyme complex). We applied our adapted occupancy modeling to a case study examining methane cycling capacity. Our models show methanogens and methanotrophs are both more likely to cooccur than be present in the absence of the other guild. The lack of consistent and complete metadata is a significant hurdle for increasing the statistical rigor of metagenomic analyses.
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10
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MbnC is not required for the formation of the N-terminal oxazolone in the methanobactin from Methylosinus trichosporium OB3b. Appl Environ Microbiol 2021; 88:e0184121. [PMID: 34731053 PMCID: PMC8788703 DOI: 10.1128/aem.01841-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Methanobactins (MBs) are ribosomally synthesized and post-translationally modified peptides (RiPPs) produced by methanotrophs for copper uptake. The post-translational modification that define MBs is the formation of two heterocyclic groups with associated thioamines from X-Cys dipeptide sequences. Both heterocyclic groups in the MB from Methylosinus trichosporium OB3b (MB-OB3b) are oxazolone groups. The precursor gene for MB-OB3b, mbnA, which is part of a gene cluster that contains both annotated and unannotated genes. One of those unannotated genes, mbnC, is found in all MB operons, and in conjunction with mbnB, is reported to be involved in the formation of both heterocyclic groups in all MBs. To determine the function of mbnC, a deletion mutation was constructed in M. trichosporium OB3b, and the MB produced from the ΔmbnC mutant was purified and structurally characterized by UV-visible absorption spectroscopy, mass spectrometry and solution NMR spectroscopy. MB-OB3b from ΔmbnC was missing the C-terminal Met and also found to contain a Pro and a Cys in place of the pyrrolidiny-oxazolone-thioamide group. These results demonstrate MbnC is required for the formation of the C-terminal pyrrolidinyl-oxazolone-thioamide group from the Pro-Cys dipeptide, but not for the formation of the N-terminal 3-methylbutanol-oxazolone-thioamide group from the N-terminal dipeptide Leu-Cys. IMPORTANCE A number of environmental and medical applications have been proposed for MBs, including bioremediation of toxic metals, nanoparticle formation, as well as for the treatment of copper- and iron-related diseases. However, before MBs can be modified and optimized for any specific application, the biosynthetic pathway for MB production must be defined. The discovery that mbnC is involved in the formation of the C-terminal oxazolone group with associated thioamide but not for the formation of the N-terminal oxazolone group with associated thioamide in M. trichosporium OB3b suggests the enzymes responsible for post-translational modification(s) of the two oxazolone groups are not identical.
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