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
Aerobic 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.
- Award ID(s):
- 1912482
- PAR ID:
- 10546442
- Editor(s):
- Zhou, Ning-Yi
- Publisher / Repository:
- American Society for Microbiology
- Date Published:
- Journal Name:
- Applied and Environmental Microbiology
- Volume:
- 89
- Issue:
- 12
- ISSN:
- 0099-2240
- Subject(s) / Keyword(s):
- methanotrophy, copper, methane monooxygenase, methanobactin, MmoD
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
ABSTRACT Aerobic methanotrophs have long been known to play a critical role in the global carbon cycle, being capable of converting methane to biomass and carbon dioxide. Interestingly, these microbes exhibit great sensitivity to copper and rare-earth elements, with the expression of key genes involved in the central pathway of methane oxidation controlled by the availability of these metals. That is, these microbes have a “copper switch” that controls the expression of alternative methane monooxygenases and a “rare-earth element switch” that controls the expression of alternative methanol dehydrogenases. Further, it has been recently shown that some methanotrophs can detoxify inorganic mercury and demethylate methylmercury; this finding is remarkable, as the canonical organomercurial lyase does not exist in these methanotrophs, indicating that a novel mechanism is involved in methylmercury demethylation. Here, we review recent findings on methanotrophic interactions with metals, with a particular focus on these metal switches and the mechanisms used by methanotrophs to bind and sequester metals.more » « less
-
Abstract Methane capture via oxidation is considered one of the ‘Holy Grails’ of catalysis (Tucci and Rosenzweig, 2024). Methane is also a primary greenhouse gas that has to be reduced by 1.2 billion metric tonnes in 10 years to decrease global warming by only 0.23°C (He and Lidstrom, 2024); hence, new technologies are needed to reduce atmospheric methane levels. In Nature, methane is captured aerobically by methanotrophs and anaerobically by anaerobic methanotrophic archaea; however, the anaerobic process dominates. Here, we describe the history and potential of using the two remarkable enzymes that have been cloned with activity for capturing methane: aerobic capture via soluble methane monooxygenase and anaerobic capture via methyl‐coenzyme M reductase. We suggest these two enzymes may play a prominent, sustainable role in addressing our current global warming crisis.
-
Particulate methane monooxygenase (pMMO), a membrane-bound enzyme having three subunits (α, β, and γ) and copper-containing centers, is found in most of the methanotrophs that selectively catalyze the oxidation of methane into methanol. Active sites in the pMMO of Methylosinus trichosporium OB3b were determined by docking the modeled structure with ethylbenzene, toluene, 1,3-dibutadiene, and trichloroethylene. The docking energy between the modeled pMMO structure and ethylbenzene, toluene, 1,3-dibutadiene, and trichloroethylene was −5.2, −5.7, −4.2, and −3.8 kcal/mol, respectively, suggesting the existence of more than one active site within the monomeric subunits due to the presence of multiple binding sites within the pMMO monomer. The evaluation of tunnels and cavities of the active sites and the docking results showed that each active site is specific to the radius of the substrate. To increase the catalysis rates of methane in the pMMO of M. trichosporium OB3b, selected amino acid residues interacting at the binding site of ethylbenzene, toluene, 1,3-dibutadiene, and trichloroethylene were mutated. Based on screening the strain energy, docking energy, and physiochemical properties, five mutants were downselected, B:Leu31Ser, B:Phe96Gly, B:Phe92Thr, B:Trp106Ala, and B:Tyr110Phe, which showed the docking energy of −6.3, −6.7, −6.3, −6.5, and −6.5 kcal/mol, respectively, as compared to the wild type (−5.2 kcal/mol) with ethylbenzene. These results suggest that these five mutants would likely increase methane oxidation rates compared to wild-type pMMO.more » « less
-
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.
-
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.more » « less