Methane-oxidizing Bacteria Species Research Articles

Screening methane-oxidizing bacteria from municipal solid waste landfills and simulating their effects on methane and ammonia reduction.

Municipal solid waste landfills are not only a crucial source of global greenhouse gas emissions; they also produce large amounts of ammonia (NH3), hydrogen sulfide, and other odorous gases that negatively affect the regional environment. Several types of methane-oxidizing bacteria (MOB) were proved to be effective in mitigating methane emission from landfills. Nevertheless, more MOB species and their technical parameters for best mitigating methane still need to be explored. In landfills, methane is simultaneously generated with ammonia, which may impede the CH4 bio-oxidizing process of MOB. However, very limited studies examined the enhancement of methane reduction by introducing ammonia-oxidizing bacteria (AOB) in landfills. In this study, two enriched MOB cultures were gained from a typical municipal solid waste landfill, and then were cultured with three strains of ammonia-oxidizing bacteria (AOB). The MOB enrichment culture used in this work includes Methylocaldum, Methylocystaceae, and Methyloversatilis, with a methane oxidation capacity of 43.6-65.0%, and the AOB includes Candida ethanolica, Bacillus cereus, and Alcaligenes faecalis. The effects on the emission reduction of both NH3 and CH4 were measured using self-made landfill-simulating equipment, as MOB, AOB, and a MOB-AOB mixture were added to the soil cover of the simulation equipment. The concentrations of CH4 and NH3 in the MOB-AOB mixture group decreased sharply, and the CH4 and NH3 concentration was 76.4% and 83.7% of the control group level. We also found that addition of AOB can help MOB oxidize CH4 and improve the emission reduction effect.

Aerobic methane oxidation under copper scarcity in a stratified lake

Aerobic methane-oxidizing bacteria (MOB) substantially reduce methane fluxes from freshwater sediments to the atmosphere. Their metalloenzyme methane monooxygenase (MMO) catalyses the first oxidation step converting methane to methanol. Its most prevalent form is the copper-dependent particulate pMMO, however, some MOB are also able to express the iron-containing, soluble sMMO under conditions of copper scarcity. So far, the link between copper availability in different forms and biological methane consumption in freshwater systems is poorly understood. Here, we present high-resolution profiles of MOB abundance and pMMO and sMMO functional genes in relation to copper, methane and oxygen profiles across the oxic-anoxic boundary of a stratified lake. We show that even at low nanomolar copper concentrations, MOB species containing the gene for pMMO expression are present at high abundance. The findings highlight the importance of copper as a micronutrient for MOB species and the potential usage of copper acquisition strategies, even under conditions of abundant iron, and shed light on the spatial distribution of these microorganisms.

Aerobic and anaerobic methanotrophic communities in urban landscape wetland.

Both aerobic methane-oxidizing bacteria (MOB) and nitrite-dependent anaerobic methane oxidation (n-damo) organisms can be important methane sinks in a wetland. However, the influences of the vegetation type on aerobic MOB and n-damo communities in wetland, especially in constructed wetland, remain poorly understood. The present study investigated the influences of the vegetation type on both aerobic MOB and n-damo organisms in a constructed urban landscape wetland. Sediments were collected from eight sites vegetated with different plant species. The abundance (1.19-3.27×107 pmoA gene copies per gram dry sediment), richness (Chao1 estimator =16.3-81.5), diversity (Shannon index =2.10-3.15), and structure of the sediment aerobic MOB community were found to vary considerably with sampling site. In contrast, n-damo community abundance (8.74×105-4.80×106 NC10 16S rRNA gene copies per gram dry sediment) changed slightly with the sampling site. The richness (Chao1 estimator =1-11), diversity (Shannon index =0-0.78), and structure of the NC10 16S rRNA gene-based n-damo community illustrated slight site-related changes, while the spatial changes of the pmoA gene-based n-damo community richness (Chao1 estimator =1-8), diversity (Shannon index =0-0.99), and structure were considerable. The vegetation type could have a profound impact on the wetland aerobic MOB community and had a stronger influence on the pmoA-based n-damo community than on the NC10 16S-based one in urban wetland. Moreover, the aerobic MOB community had greater abundance and higher richness and diversity than the n-damo community. Methylocystis (type II MOB) predominated in urban wetland, while no known type I MOB species was detected. In addition, the ratio of total organic carbon to total nitrogen (C/N) might be a determinant of sediment n-damo community diversity and aerobic MOB richness.

Isolation of methanotrophic bacteria from termite gut

The guts of termites feature suitable conditions for methane oxidizing bacteria (MOB) with their permanent production of CH4 and constant supply of O2via tracheae. In this study, we have isolated MOB from the gut contents of the termites Incisitermes marginipennis, Mastotermes darwiniensis, and Neotermes castaneus for the first time. The existence of MOB was indicated by detecting pmoA, the gene for the particulate methane monooxygenase, in the DNA of gut contents. Fluorescence in situ hybridization and quantitative real-time polymerase chain reaction supported those findings. The MOB cell titer was determined to be 102–103 per gut. Analyses of the 16S rDNA from isolates indicated close similarity to the genus Methylocystis. After various physiological tests and fingerprinting methods, no exact match to a known species was obtained, indicating the isolation of new MOB species. However, MALDI-TOF MS analyses revealed a close relationship to Methylocystis bryophila and Methylocystis parvus.

A reanalysis of phospholipid fatty acids as ecological biomarkers for methanotrophic bacteria

Aerobic methane-oxidizing bacteria (MB) are the primary terrestrial sinks for the greenhouse gas methane. A distinct characteristic of MB is the presence of specific phospholipid ester-linked fatty acids (PLFA) in their membranes that differentiate them from each other and also from all other organisms. These distinct PLFA patterns facilitate microbial ecology studies. For example, the assimilation of C from methane into PLFA can be traced in environmental samples using stable isotope ((13)C) probing (SIP), which links the activity of MB to their community composition in situ. However, the phylogenetic resolution of this method is low because of a lack of PLFA profiles from cultured MB species. In this study, PLFA profiles of 22 alphaproteobacterial (type II) MB were analysed after growth on methane, methanol or both substrates together. Growth on different substrates did not affect the PLFA profiles of the investigated strains. A number of Methylocystis strains contained novel C18:2 fatty acids (omega 7c,12c and omega 6c,12c) that can be used as diagnostic biomarkers. The detection of these novel PLFA, combined with the analyses of multiple type II strains, increased the phylogenetic resolution of PLFA analysis substantially. Multivariate analysis of the expanded MB PLFA database identified species groups that closely reflected phylogenies based on 16S rRNA and pmoA gene sequences. The PLFA database therefore provides a robust framework for linking identity to activity in MB communities with a higher resolution than was previously possible.

Molecular phylogeny of type II methane-oxidizing bacteria isolated from various environments.

Type II methane-oxidizing bacteria (MOB) were isolated from diverse environments, including rice paddies, pristine and polluted freshwaters and sediments, mangrove roots, upland soils, brackish water ecosystems, moors, oil wells, water purification systems and livestock manure. Isolates were identified based on morphological traits as either Methylocystis spp., Methylosinus sporium or Methylosinus trichosporium. Molecular phylogenies were constructed based on nearly complete 16S rRNA gene sequences, and on partial sequences of genes encoding PmoA (a subunit of particulate methane monooxygenase), MxaF (a subunit of methanol dehydrogenase) and MmoX (a subunit of soluble methane monooxygenase). The maximum pairwise 16S rDNA difference between isolates was 4.2%, and considerable variability was evident within the Methylocystis (maximum difference 3.6%). Due to this variability, some of the published 'specific' oligonucleotide primers for type II MOB exhibit multiple mismatches with gene sequences from some isolates. The phylogenetic tree constructed from pmoA gene sequences closely mirrored that constructed from 16S rDNA sequences, and both supported the presently accepted taxonomy of type II MOB. Contrary to previously published phylogenetic trees, morphologically distinguishable species were generally monophyletic based on pmoA or 16S rRNA gene sequences. This was not true for phylogenies constructed from mmoX and mxaF gene sequences. The phylogeny of mxaF gene sequences suggested that horizontal transfer of this gene may have occurred across type II MOB species. Soluble methane monooxygenase could not be detected in many Methylocystis strains either by an enzyme activity test (oxidation of naphthalene) or by PCR-based amplification of an mmoX gene.

Methylobacterium, a New Genus of Facultatively Methylotrophic Bacteria

A new genus and a new species of methane-oxidizing bacteria are described. The colonies produced by these bacteria are pink, circular, and convex with entire margins. Cells are gram negative and are normally found singularly with some rosettes. Negative stains indicate polar flagellation. In thin sections, intracytoplasmic membranes, similar to those described as type II in other methylotrophs, were present when the cells were grown with methane. No such membranes were apparent when the cells were grown with the other carbon and energy sources tested. The serine pathway for formaldehyde incorporation is the pathway of C1 metabolism. The deoxyribonucleic acid base composition is 66 mol% guanine plus cytosine. Methylobacterium is proposed as the name for this new genus of rod-shaped, methane-oxidizing bacteria. The specific epithet in the name of the type species, Methylobacterium organophilum sp. nov., denotes the preference of this organism for organic carbon and energy sources more complex than methane. The type strain of M. organophilum is XX (= ATCC 27886). This bacterium differs from all previously described genera and species of methane-oxidizing bacteria in its ability to utilize a variety of organic substrates with carbon-carbon bonds as sources of carbon and energy. The pathways for methane oxidation and the assimilation of one-carbon units are repressed during growth on complex organic substrates.

Identification of 2-amino-4-hydroxy-6-methylpteridine as a naturally-occurring compound in two methane·oxidizing bacteria

Four pteridines have been isolated from two species of methane-oxidizing bacteria. They are: 2-amino-4-hydroxy-6-carboxypteridine, D- erythro -neopterin, 2-amino-4-hydroxypteridine, and 2-amino-4-hydroxy-6-methylpteridine. This latter compound has not previously been shown to occur naturally.