The regulation of rhizosphere bacterial community structure and metabolism by plants in municipal solid waste landfills is a key to enhancing the biodegradation of chlorobenzene (CB). In this study, we employed biodiversity and metabolomics methods to systematically analyze the mechanisms of different plant species in regulating the rhizosphere bacterial community structure and metabolic features and then improved the methane (CH₄) oxidation and CB degradation capacity. The results showed that the rhizosphere soil of Rumex acetosa exhibited the highest CH₄ oxidation and CB degradation capacity of 0.08 g/(kg·h) and 1.72×10^-6 g/(L·h), respectively, followed by the rhizosphere soil of Amaranthus spinosus L., with the rhizosphere soil of Broussonetia papyrifera showing the weakest activity. Rumex acetosa promoted the colonization of Methylocaldum in the rhizosphere, and the small-molecule organic amine, such as triethylamine and N-methyl-aniline, secreted from the roots of this plant enhanced the tricarboxylic acid cycle and nicotinamide metabolism, thereby increasing microbial activity and improving CH₄ and CB degradation efficiency. Conversely, cinnamic acid and its derivatives secreted by Broussonetia papyrifera acted as autotoxins, inhibiting microbial activity and exacerbating the negative effects of salt stress on key microbes such as methanotrophs. This study probed into the mechanisms of typical plants growing in landfill cover soil in regulating bacterial ecological functions, offering theoretical support and practical guidance for the plant-microbe joint control of landfill gas pollution.
Biodegradation, Environmental ; Rhizosphere ; Soil Microbiology ; Waste Disposal Facilities ; Chlorobenzenes/metabolism* ; Bacteria/metabolism* ; Soil Pollutants/metabolism* ; Methane/metabolism* ; Plant Roots/microbiology* ; Amaranthus/microbiology* ; Soil

Arsenic (As) is a common toxic pollution element. The microorganism-mediated transformation of arsenic forms is an important part in the biogeochemical cycle of As. In the various microbial metabolic processes involving As, the coupling reduction of As has a great impact on the environment and is a process that is easily overlooked. From the biogeochemical cycle of As, this review introduces the microorganism-mediated methane oxidation, anaerobic ammonium oxidation, and iron (Fe)-sulfur (S) oxidation coupled with As reduction. Organic matter, pH, and redox potential are the main factors affecting the coupling reduction. After the coupling reduction, the toxicity and migration of As are greatly enhanced, which may increase the risk of As pollution. Therefore, it is of great significance to clarify the influences of carbon, nitrogen, Fe, S and other elements on the coupling process and explore more microbial processes coupled with As reduction for the prevention and control of As pollution.
Arsenic/metabolism* ; Oxidation-Reduction ; Bacteria/metabolism* ; Environmental Pollutants/metabolism* ; Biodegradation, Environmental ; Methane/metabolism* ; Iron/metabolism* ; Ammonium Compounds/metabolism*

Aerobic methane oxidizing bacteria (methanotrophs) can use methane as carbon source and energy source, eliminating 10%-20% of global methane. Methanotrophs can also effectively synthesize valuable methane-derived products. This article introduced the methane oxidizing mechanism of methanotrophs, and summarized the practical application and research hotspots of methanotrophs in the field of methane emission reduction in the landfill, ventilation air methane mitigation in coal mines, valuable chemicals biosynthesis, as well as oil and gas reservoir exploration. Main factors influencing the pollutant removal and the biosynthesis efficiency in various applications were also discussed. Based on the study of large-scale cultivation of methanotrophs, some measures to benefit the application and promotion of aerobic methane oxidizing biotechnology were proposed. This includes investigating the effect of intermediate metabolites on methanotrophs activity and population structure, and exploiting economical and efficient alternative culture media and culture techniques.
Biotechnology ; Carbon ; Culture Media/chemistry* ; Methane/metabolism* ; Methylococcaceae/metabolism* ; Oxidation-Reduction

Landfill is one of the important sources of carbon tetrachloride (CT) pollution, and it is important to understand the degradation mechanism of CT in landfill cover for better control. In this study, a simulated landfill cover system was set up, and the biotransformation mechanism of CT and the associated micro-ecology were investigated. The results showed that three stable functional zones along the depth, i.e., aerobic zone (0-15 cm), anoxic zone (15-45 cm) and anaerobic zone (> 45 cm), were generated because of long-term biological oxidation in landfill cover. There were significant differences in redox condition and microbial community structure in each zone, which provided microbial resources and favorable conditions for CT degradation. The results of biodegradation indicated that dechlorination of CT produced chloroform (CF), dichloromethane (DCM) and Cl^- in anaerobic and anoxic zones. The highest concentration of dechlorination products occurred at 30 cm, which were degraded rapidly in aerobic zone. In addition, CT degradation rate was 13.2-103.6 μg/(m²·d), which decreased with the increase of landfill gas flux. The analysis of diversity sequencing revealed that Mesorhizobium, Thiobacillus and Intrasporangium were potential CT-degraders in aerobic, anaerobic and anoxic zone, respectively. Moreover, six species of dechlorination bacteria and eighteen species of methanotrophs were also responsible for anaerobic transformation of CT and aerobic degradation of CF and DCM, respectively. Interestingly, anaerobic dechlorination and aerobic transformation occurred simultaneously in the anoxic zone in landfill cover. Furthermore, analysis of degradation mechanism suggested that generation of stable anaerobic-anoxic-aerobic zone by regulation was very important for the harmless removal of full halogenated hydrocarbon in vadose zone, and the increase of anoxic zone scale enhanced their removal. These results provide theoretical guidance for the removal of chlorinated pollutants in landfills.
Bacteria/metabolism* ; Biodegradation, Environmental ; Carbon Tetrachloride/metabolism* ; Methane/metabolism* ; Waste Disposal Facilities

Methanogens are unique microorganisms for methane production and the main contributor of the biogenic methane in atmosphere. Methyl-coenzyme M reductase (Mcr) catalyzes the last step of methane production in methanogenesis and the first step of methane activation in anaerobic oxidation of methane. The genes encoding this enzyme are highly conserved and are widely used as a marker in the identification and phylogenetic study of archaea. There has been a longstanding interest in its unique cofactor F430 and the underpinning mechanisms of enzymatic cleavage of alkane C-H bond. The recent breakthroughs of high-resolution protein and catalytic-transition-state structures further advanced the structure-function study of Mcr. In particular, the recent discovery of methyl-coenzyme M reductase-like (Mcr-like) enzymes that activates the anaerobic degradation of non-methane alkanes has attracted much interest in the molecular mechanisms of C-H activation without oxygen. This review summarized the advances on function-structure-mechanism study of Mcr/Mcr-like enzymes. Additionally, future directions in anaerobic oxidation of alkanes and greenhouse-gas control using Mcr/Mcr-like enzymes were proposed.
Archaea/metabolism* ; Methane ; Oxidation-Reduction ; Oxidoreductases/metabolism* ; Phylogeny

BACKGROUND: Asthma is a common cause of breathing difficulty in children and adults, and is characterized by chronic airway inflammation that is poorly controlled by available treatments. This results in severe disability and applies a huge burden to the public health system. Methane has been demonstrated to function as a therapeutic agent in many diseases. The aim of the present study was to explore the effect of methane-rich saline (MRS) on the pathophysiology of a mouse model of asthma and its underlying mechanism. METHODS: A murine model of ovalbumin (OVA)-induced allergic asthma was applied in this study. Mice were divided into three groups: a control group, an OVA group, and OVA-induced asthmatic mice treated with MRS as the third group. Lung resistance index (RI) and dynamic compliance (Cdyn) were measured to determine airway hyper-responsiveness (AHR). Haematoxylin and eosin (H&E) staining was performed and scored to show histopathological changes. Cell counts of bronchoalveolar lavage fluid (BALF) were recorded. Cytokines interleukin (IL)-4, IL-5, IL-13, tumor necrosis factor α (TNF-α), and C-X-C motif chemokine ligand 15 (CXCL15) from BALF and serum were measured by enzyme-linked immunosorbent assay (ELISA). The oxidative stress indexes, including malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), myeloperoxidase (MPO), and 8-hydroxydeoxyguanosine (8-OHdG), were determined using commercial kits. Apoptosis was evaluated by western blot, quantitative real-time polymerase chain reaction (qRT-PCR), and biochemical examination. RESULTS: MRS administration reversed the OVA-induced AHR, attenuated the pathological inflammatory infiltration, and decreased the cytokines IL-4, IL-5, IL-13, TNF-α, and CXCL15 in serum and BALF. Moreover, following MRS administration, the oxidative stress was alleviated as indicated by decreased MDA, MPO, and 8-OHdG, and elevated SOD and GSH. In addition, MRS exhibited an anti-apoptotic effect in this model, protecting epithelial cells from damage. CONCLUSIONS Methane improves pulmonary function and decreases infiltrative inflammatory cells in the allergic asthmatic mouse model. This may be associated with its anti-inflammatory, antioxidative, and anti-apoptotic properties.
Animals ; Apoptosis/drug effects* ; Asthma/metabolism* ; Bronchial Hyperreactivity/drug therapy* ; Cytokines/analysis* ; Female ; Inflammation/prevention & control* ; Methane/pharmacology* ; Mice ; Mice, Inbred BALB C ; Oxidative Stress/drug effects* ; Saline Solution

Methane monooxygenases (MMO), regarded as "an amazing biomolecular machine", catalyze the oxidation of methane to methanol under aerobic conditions. MMO catalyze the oxidation of methane elaborately, which is a novel way to catalyze methane to methanol. Furthermore, MMO can inspire the biomolecular machine design. In this review, we introduced MMO including structure, gene and catalytic mechanism. The history and the taxonomy of MMO were also introduced.
Catalysis ; Methane ; metabolism ; Methanol ; metabolism ; Oxygenases ; metabolism

In order to understand metabolic functions essential for methane assimilation, we investigate dribulose monophosphate pathway and adjacent pathways in gammaproteobacterial Methylomicrobium alcaliphilum 20Z by using combined approaches of RNA-seq, LC-MS, and 13C-labeled techniques. The absolute quantification of metabolome showed that the concentrations of intermediates, such as glucose-6-phosphate and 2-dehydro-3-deoxy-phosphogluconate, involved in Entner-Doudoroff (EDD) pathway were (150.95 +/- 28.75) micromol/L and below the limit of detection of mass spectrometry. In contrast, fructose-1, 6-bisphosphate, glyceraldehyde-3-phosphate/dihydroxyacetone and phosphoenolpyruvate in Embden-Meyerhof-Parnas (EMP) pathway had significantly higher concentrations with (1 142.02 +/- 302.88) micromol/L, (1 866.76 +/- 388.55) micromol/L and (3 067.57 +/- 898.13) micromol/L, respectively. 13C-labeling experiment further indicated that the enrichment of [3-13C1]-pyruvate involved in EMP pathway was 4-6 fold higher than [1,13C1]-pyruvate in EDD pathway in a dynamic course. Moreover, gene expression profile showed that the expression levels of genes in EMP pathway (e.g. fbaA, tpiA, gap and pykA) were 2 479.2, 2 493.9, 2 274.6 and 1 846.0, respectively, but gene expressionlevels in EDD pathway (e.g. pgi, eda and edd) were only 263.8, 341.2 and 225.4, respectively. Overall our current results demonstrated that EMP pathway was the main route for methane assimilation in M. alcaliphilum 20Z. This discovery challenged our understanding of methane assimilation pathway in gammaproteobacterial methanotrophic bacteria, and further provided an important insight for efficient methane biocatalysis in the future.
Glycolysis ; Industrial Microbiology ; Methane ; metabolism ; Methylococcaceae ; metabolism ; Pyruvic Acid ; metabolism

Colocolic fistulas are usually a complication of an inflammatory or neoplastic process. Development of these abnormal bowel communications may lead to bacterial overgrowth. We report on a 71-year-old man with a one-year history of recurrent abdominal distension and irregular bowel habits. Abdominal X-rays and computed tomography showed multiple air-fluid levels and loops of distended bowel without evidence of mechanical obstruction or diverticulitis. Colonoscopy showed a fistulous tract between the sigmoid colon and cecum. Results of a lactulose breath test showed high fasting breath CH4 levels, which were thought to be the result of intestinal bacterial overgrowth. The patient was diagnosed with a colonic pseudo-obstruction associated with bacterial overgrowth due to a sigmoidocecal fistula. We recommended surgical correction of the sigmoidocecal fistula; however, the patient requested medical treatment. After antibiotic therapy, the patient still had mild symptoms but no acute exacerbations.
Aged ; Anti-Bacterial Agents/therapeutic use ; Breath Tests ; Colonic Pseudo-Obstruction/*diagnosis/etiology ; Colonoscopy ; Humans ; Intestinal Fistula/*diagnosis/drug therapy/microbiology ; Male ; Methane/chemistry/metabolism ; Tomography, X-Ray Computed

Whether hydrogen and methane gas produced during lactulose breath test (LBT) are associated with symptoms of irritable bowel syndrome (IBS) is not determined. We aimed to investigate whether hydrogen and methane on LBT are associated with IBS symptoms. Sixty-eight IBS patients meeting the Rome III criteria for IBS, and 55 healthy controls, underwent LBT. The IBS subjects recorded their customary gastrointestinal symptoms on a questionnaire using visual analogue scales. LBT positivity was defined to be above 20 ppm rise of hydrogen or 10 ppm rise of methane within 90 min. Gas amounts produced during LBT were determined by calculating area under the curve of hydrogen and methane excretion. Symptom severity scores were not different between the LBT (+) IBS and LBT (-) IBS subjects and also between methane producers and non-methane producers. Gas amounts produced during LBT were not associated with IBS symptoms, except a weak correlation between total gas amounts and a few IBS symptoms such as bloating (r = 0.324, P = 0.039), flatulence (r = 0.314, P = 0.046) and abdominal pain (r = 0.364, P = 0.018) only in LBT (+) IBS. In conclusion, hydrogen and methane gas on LBT are not useful for predicting the customary symptoms and subtypes of IBS.
Abdominal Pain/etiology ; Adult ; Area Under Curve ; Breath Tests ; Female ; Flatulence/etiology ; Gases/analysis ; Humans ; Hydrogen/*analysis ; Irritable Bowel Syndrome/*diagnosis ; Lactulose/*metabolism ; Male ; Methane/*analysis ; Middle Aged ; ROC Curve ; Risk Factors