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1. Methane-oxidizing bacterial community dynamics in sub-alpine forest soil

   https://doi.org/10.1128/spectrum.00834-24  

   Beals, Delaney G; Munn, J Jackson; Puri, Aaron W (November 2024, Microbiology Spectrum)

   Reverchon, Frédérique (Ed.)

   ABSTRACT Microbial activities in sub-alpine forest soil influence global cycling of the potent greenhouse gas methane. Understanding the dynamics of methane-oxidizing bacterial communities, particularly the roles of potentially active versus total microbial populations, is necessary for reducing uncertainty in global methane budget estimates. However, our understanding of the factors influencing methane cycling in forest soils is limited by our lack of knowledge about the biology of the microbes involved and how these communities are shaped by their environment. Here, we compared the composition and potential activity of microbial communities using 16S rRNA gene amplicon sequencing of total genomic DNA (gDNA) and potentially active complementary DNA (cDNA) from shallow soil in Red Butte Canyon (Salt Lake City, Utah, USA). We compared riparian and upland soils at two time points in the growing season and found distinct differences in both the community composition of the gDNA and cDNA libraries and the potential drivers of these community structures. Aerobic methane-oxidizing bacteria (methanotrophs) were detected in all samples, with cDNA libraries containing a higher average relative abundance and diversity of methanotrophs compared to gDNA libraries. Methane flux at the sample sites did not significantly correlate to the relative abundance (gDNA) or potential activity (cDNA) of methanotrophs. In the cDNA libraries, there were significant positive correlations between the abundance ofMethylococcaceaefamily methanotrophs and several non-methanotrophic methylotrophs previously found to be associated with methane-oxidizing bacterial communities. These findings suggest a complex relationship between methane-cycling bacterial communities and methane flux and highlight the need for furtherin situstudies to understand the environmental and ecological influences of these microbial consortia. IMPORTANCEMethane-oxidizing bacteria are found in diverse soil and sediment environments and play an important role in mitigating flux of this potent greenhouse gas into the atmosphere. However, it is unclear how these bacteria and their associated communities are structured in the environment and how their activity ultimately influences methane flux. In this work, we examine the composition and structure of methane-oxidizing bacterial communities in sub-alpine forest soil and find soil- and time-specific differences between the stable and potentially active populations. We also find that the potentially active populations of certain methanotrophs and non-methanotrophs are positively correlated. This work provides a step toward refining our understanding of microbially mediated biogeochemical cycles. 

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2. Identifying Active Methanotrophs and Mitigation of CH4 Emissions in Landfill Cover Soil

   https://doi.org/10.1007/978-981-13-2224-2_38  

   Rai, R.K.; Chetri, J.K.; Green, S.J.; Reddy, K.R. (January 2019, Proc. 8th International Congress on Environmental Geotechnics)

   In the USA, municipal solid waste (MSW) landfills constitute one of the major anthropogenic sources of methane emissions. In the landfill cover soils employed at MSW landfills, aerobic methane-oxidizing bacteria (MOB) convert CH4 to CO2, thereby partially mitigating the CH4 emissions to the atmosphere. In this study, culture-dependent and culture-independent techniques were employed to evaluate methane oxidation capacity and to characterize the microbial community in landfill cover soil. Microcosms with synthetic landfill gas headspace were used to measure potential methane oxidation rates in landfill cover soil and in methanotrophs-enriched microbial consortia. The results demonstrate that the enriched landfill cover soil supported the growth of a diverse group of methanotrophic and methylotrophic microorganisms, and were dominated by Type I methanotrophs showing positive correlation with CH4 oxidation rates. 

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3. MmoD regulates soluble methane monooxygenase and methanobactin production in Methylosinus trichosporium OB3b

   https://doi.org/10.1128/aem.01601-23  

   Peng, Peng; Yang, Junwon; DiSpirito, Alan A; Semrau, Jeremy D (December 2023, Applied and Environmental Microbiology)

   Zhou, Ning-Yi (Ed.)

   ABSTRACT Methane oxidation by aerobic methanotrophs is well known to be strongly regulated by the availability of copper, i.e., the “copper switch.” That is, there are two forms of methane monooxygenase: a cytoplasmic or soluble methane monooxygenase (sMMO) and a membrane-bound or particulate methane monooxygenase (pMMO). sMMO is only expressed and active in the absence of copper, while pMMO requires copper. Previous work has also shown that one gene in the operon of the soluble methane monooxygenase—mmoD—also plays a critical role in the “copper switch,” but its function is still vague. Herein, we show that MmoD is not needed for the expression of genes in the sMMO gene cluster but is critical for the formation of sMMO polypeptides and sMMO activity inMethylosinus trichosporiumOB3b, indicating that MmoD plays a key post-transcriptional role in the maturation of sMMO. Furthermore, data also show that MmoD controls the expression of methanobactin, a copper-binding compound used by some methanotrophs, includingM. trichosporiumOB3b, for copper sequestration. Collectively, these results provide greater insights into the components of the “copper switch” and provide new strategies to manipulate methanotrophic activity. IMPORTANCEAerobic methanotrophs play a critical role in the global carbon cycle, particularly in controlling net emissions of methane to the atmosphere. As methane is a much more potent greenhouse gas than carbon dioxide, there is increasing interest in utilizing these microbes to mitigate future climate change by increasing their ability to consume methane. Any such efforts, however, require a detailed understanding of how to manipulate methanotrophic activity. Herein, we show that methanotrophic activity is strongly controlled by MmoD, i.e., MmoD regulates methanotrophy through the post-transcriptional regulation of the soluble methane monooxygenase and controls the ability of methanotrophs to collect copper. Such data are likely to prove quite useful in future strategies to enhance the use of methanotrophs to not only reduce methane emissions but also remove methane from the atmosphere. 

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4. Oxygen Generation via Water Splitting by a Novel Biogenic Metal Ion-Binding Compound

   https://doi.org/10.1128/AEM.00286-21  

   Dershwitz, Philip; Bandow, Nathan L; Yang, Junwon; Semrau, Jeremy D; McEllistrem, Marcus T; Heinze, Rafael A; Fonseca, Matheus; Ledesma, Joshua C; Jennett, Jacob R; DiSpirito, Ana M; et al (June 2021, Applied and Environmental Microbiology)

   Parales, Rebecca E (Ed.)

   The discovery that MB will couple the oxidation of H₂O to metal ion reduction and the release of O₂suggests that methanotrophs expressing MB may be able to maintain their activity under hypoxic/anoxic conditions through the “self-generation” of dioxygen required for the initial oxidation of methane to methanol. Such an ability may be an important factor in enabling methanotrophs to not only colonize the oxic-anoxic interface where methane concentrations are highest but also tolerate significant temporal fluctuations of this interface. 

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5. Methane Removal from Air: Challenges and Opportunities

   https://doi.org/10.3390/methane2040027  

   Wang, Jin; He, Qinghua Peter (December 2023, Methane)

   Driven by increasing greenhouse gas (GHG) concentrations in the atmosphere, extreme weather events have become more frequent and their impacts on human lives have become more severe. Therefore, the need for short-term GHG mitigations is urgent. Recently, methane has been recognized as an important mitigation target due to its high global warming potential (GWP). However, methane’s low concentration in the atmosphere and stable molecular structure make its removal from the air highly challenging. This review first discusses the fundamental aspects of the challenges in atmospheric methane removal and then briefly reviews the existing research strategies following the mechanisms of natural methane sinks. Although still in its infancy, recent research on methane removal from the air holds great potential for slowing down global warming. At the same time, it is important to carefully examine the energy consumption of these methane removal strategies and whether they will be able to achieve net GHG reduction. In addition, due to the scale of methane removal from the air, any potential solution’s environmental impacts must be carefully evaluated before it can be implemented in practice. 

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