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Selenium-binding protein 1 (SELENBP1) has been associated with several cancers, although its exact role is unknown. We show that SELENBP1 is a methanethiol oxidase (MTO), related to the MTO in methylotrophic bacteria, that converts methanethiol to H 2 O 2 , formaldehyde, and H 2 S, an activity not previously known to exist in humans. We identified mutations in SELENBP1 in five patients with cabbage-like breath odor. The malodor was attributable to high levels of methanethiol and dimethylsulfide, the main odorous compounds in their breath. Elevated urinary excretion of dimethylsulfoxide was associated with MTO deficiency. Patient fibroblasts had low SELENBP1 protein levels and were deficient in MTO enzymatic activity; these effects were reversed by lentivirus-mediated expression of wild-type SELENBP1 . Selenbp1 -knockout mice showed biochemical characteristics similar to those in humans. Our data reveal a potentially frequent inborn error of metabolism that results from MTO deficiency and leads to a malodor syndrome. Ron Wevers and colleagues report that mutations in the methanethiol oxidase gene SELENBP1 cause chronic extraoral halitosis. They find that enzyme deficiency leads to increased levels of methanethiol and dimethylsulfide in the breath and that knockout mice have similar biochemical phenotypes.

This study overthrows a long-time assumption that methanethiol oxidases (MTOs) cleave the C–S bond of methanethiol to produce both H 2 S and H 2 O 2 —the former is a strong reductant and the latter is a strong oxidant. From a chemistry viewpoint, this reaction is difficult to happen. Investigations on three representative MTOs indicated that sulfane sulfur (S 0 ) was the direct product, and no H 2 O 2 was produced. Finally, the products of MTOs were corrected to be S 0 and H 2 O. This finding connected dimethylsulfoniopropionate (DMSP) degradation with sulfane sulfur metabolism, filling a critical gap in the DMSP degradation pathway and representing new knowledge in the marine sulfur cycle field.

The structure-activity relationship in catalytic ozonation remains unclear, hindering the understanding of activity origins. Here, we report activity trends in catalytic ozonation using a series of single-atom catalysts with well-defined M 1 -N 3 C 1 (M: manganese, ferrum, cobalt, and nickel) active sites. The M 1 -N 3 C 1 units induce locally polarized M − C bonds to capture ozone molecules onto M atoms and serve as electron shuttles for catalytic ozonation, exhibiting excellent catalytic activities (at least 527 times higher than commercial manganese dioxide). The combined in situ characterization and theoretical calculations reveal single metal atom-dependent catalytic activity, with surface atomic oxygen reactivity identified as a descriptor for the structure-activity relationship in catalytic ozonation. Additionally, the dissociation barrier of surface peroxide species is proposed as a descriptor for the structure-activity relationship in ozone decomposition. These findings provide guidelines for designing high-performance catalytic ozonation catalysts and enhance the atomic-level mechanistic understanding of the integral control of ozone and methyl mercaptan. Understanding the atomic-level structure-activity relationship in catalytic ozonation is crucial. Here, the authors reveal single-metal-atom-dependent catalytic ozonation and identify surface atomic oxygen reactivity as a descriptor in this relationship.

Oxidation of methanethiol (MT) is a significant step in the sulfur cycle. MT is an intermediate of metabolism of globally significant organosulfur compounds including dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS), which have key roles in marine carbon and sulfur cycling. In aerobic bacteria, MT is degraded by a MT oxidase (MTO). The enzymatic and genetic basis of MT oxidation have remained poorly characterized. Here, we identify for the first time the MTO enzyme and its encoding gene ( mtoX ) in the DMS-degrading bacterium Hyphomicrobium sp. VS. We show that MTO is a homotetrameric metalloenzyme that requires Cu for enzyme activity. MTO is predicted to be a soluble periplasmic enzyme and a member of a distinct clade of the Selenium-binding protein (SBP56) family for which no function has been reported. Genes orthologous to mtoX exist in many bacteria able to degrade DMS, other one-carbon compounds or DMSP, notably in the marine model organism Ruegeria pomeroyi DSS-3, a member of the Rhodobacteraceae family that is abundant in marine environments. Marker exchange mutagenesis of mtoX disrupted the ability of R. pomeroyi to metabolize MT confirming its function in this DMSP-degrading bacterium. In R. pomeroyi , transcription of mtoX was enhanced by DMSP, methylmercaptopropionate and MT. Rates of MT degradation increased after pre-incubation of the wild-type strain with MT. The detection of mtoX orthologs in diverse bacteria, environmental samples and its abundance in a range of metagenomic data sets point to this enzyme being widely distributed in the environment and having a key role in global sulfur cycling.

The increasing sulfur content in fossil fuels and the use of biogas as a renewable energy source has highlighted the need for effective desulfurization processes. To remove sulfur species from gaseous resources efficiently, a catalytic process that can convert sulfur compounds to hydrogen sulfide (H 2 S) at low temperatures is desirable. In this study, electric-field-assisted catalytic methanethiol (CH 3 SH) decomposition was performed to develop a new system for converting sulfur compounds to H 2 S at low temperatures. In the thermal catalytic reaction using the Pt/CeO 2 catalyst, dimethyl sulfide, which is a byproduct of the reaction, is formed. Compared with the result, applying an electric field suppressed the side reaction. The CH 4 and H 2 S formation rates slightly improved by applying the electric field, suggesting the possibility of controlling the CH 3 SH decomposition products. Graphical Abstract

Methanotrophs are able to metabolize volatile organic sulfur compounds (VOSCs), excrete organic carbon during CH4 oxidation, and influence microbial community structure and function of the ecosystem. In return, microbial community structure and environmental factors can affect the growth metabolism of methanotrophs. In this study, Methylomonas koyamae and Hyphomicrobium methylovorum were used for model organisms, and methanethiol (MT) was chosen for a typical VOSC to investigate the synergy effects under VOSC stress. The results showed that when Hyphomicrobium methylovorum was co-cultured with Methylomonas koyamae in the medium with CH4 used as the carbon source, the co-culture had better MT tolerance relative to Methylomonas koyamae and oxidized all CH4 within 120 h, even at the initial MT concentration of 2000 mg m−3. The optimal co-culture ratios of Methylomonas koyamae to Hyphomicrobium methylovorum were 4:1–12:1. Although MT could be converted spontaneously to dimethyl disulfide (DMDS), H2S, and CS2 in air, faster losses of MT, DMDS, H2S, and CS2 were observed in each strain mono-culture and the co-culture. Compared with Hyphomicrobium methylovorum, MT was degraded more quickly in the Methylomonas koyamae culture. During the co-culture, the CH4 oxidation process of Methylomonas koyamae could provide carbon and energy sources for the growth of Hyphomicrobium methylovorum, while Hyphomicrobium methylovorum oxidized MT to help Methylomonas koyamae detoxify. These findings are helpful to understand the synergy effects of Methylomonas koyamae and Hyphomicrobium methylovorum under MT stress and enrich the role of methanotrophs in the sulfur biogeochemical cycle.Key points• The co-culture of Methylomonas and Hyphomicrobium has better tolerance to CH3SH.• Methylomonas can provide carbon sources for the growth of Hyphomicrobium.• The co-culture of Methylomonas and Hyphomicrobium enhances the removal of CH4 and CH3SH.

Methane is the second most important greenhouse gas on earth. It is produced by methanogenic archaea, which play an important role in the global carbon cycle. Three main methanogenesis pathways are known: in the hydrogenotrophic pathway H2 and carbon dioxide are used for methane production, whereas in the methylotrophic pathway small methylated carbon compounds like methanol and methylated amines are used. In the aceticlastic pathway, acetate is disproportionated to methane and carbon dioxide. However, next to these conventional substrates, further methanogenic substrates and pathways have been discovered. Several phylogenetically distinct methanogenic lineages (Methanosphaera, Methanimicrococcus, Methanomassiliicoccus, Methanonatronarchaeum) have evolved hydrogen-dependent methylotrophic methanogenesis without the ability to perform either hydrogenotrophic or methylotrophic methanogenesis. Genome analysis of the deep branching Methanonatronarchaeum revealed an interesting membrane-bound hydrogenase complex affiliated with the hardly described class 4 g of multisubunit hydrogenases possibly providing reducing equivalents for anabolism. Furthermore, methylated sulfur compounds such as methanethiol, dimethyl sulfide, and methylmercaptopropionate were described to be converted into adapted methylotrophic methanogenesis pathways of Methanosarcinales strains. Moreover, recently it has been shown that the methanogen Methermicoccus shengliensis can use methoxylated aromatic compounds in methanogenesis. Also, tertiary amines like choline (N,N,N-trimethylethanolamine) or betaine (N,N,N-trimethylglycine) have been described as substrates for methane production in Methanococcoides and Methanolobus strains. This review article will provide in-depth information on genome-guided metabolic reconstructions, physiology, and biochemistry of these unusual methanogenesis pathways.Key points• Newly discovered methanogenic substrates and pathways are reviewed for the first time.• The review provides an in-depth analysis of unusual methanogenesis pathways.• The hydrogenase complex of the deep branching Methanonatronarchaeum is analyzed.

This study aimed to measure the levels of volatile sulfur compounds and investigate the occurrence of halitosis in patients with gingivitis and periodontitis. Additionally, the incidence rates of gingivitis and periodontitis in patients with halitosis were investigated. Through various statistical analyses, we attempted to determine the relationship between periodontal disease and halitosis. One-hundred-and-four participants (52 females and 52 males, mean age: 46.49 ± 16.03 years) were enrolled in this cross-sectional study, comprising 33 healthy controls, 43 patients with gingivitis, and 28 patients with periodontitis. Gas chromatography was used to measure hydrogen sulfide (H 2 S) and methyl mercaptan (CH 3 SH), which are representative VSCs. The VSC cut-off values for diagnosing halitosis were 65.79 ppb for women and 79.94 ppb for men. Total VSC level was significantly higher in the gingivitis than the healthy control group (186.72 ± 374.83 ppb vs. 19.80 ± 40.19 ppb, p = 0.035). There was no significant difference between the gingivitis and periodontitis (153.79 ± 278.51 ppb) groups. H 2 S level was significantly higher in the gingivitis (100.51 ± 183.69 ppb) and periodontitis (91.57 ± 132.06 ppb) groups than in healthy controls (14.97 ± 31.22 ppb), and CH 3 SH level was significantly higher in gingivitis group (29.31 ± 59.16 ppb) than in the healthy control (5.73 ± 14.10 ppb) (all p < 0.05). Halitosis was found in 3% of healthy controls and 39.5% and 42.9% of patients with gingivitis and periodontitis patients, respectively, making it significantly higher in the gingivitis and periodontitis groups than the healthy controls (p = 0.005). Conversely, among participants with halitosis, 53.1% had gingivitis, 37.5% had periodontitis, and 90.6 incidence had periodontal disease. Multivariate logistic regression analysis to predict the presence of halitosis, found periodontal disease was a significant predictor of halitosis (OR = 3.607, 95% CI 1.023–12.718, p = 0.046). Considering area under curve value for halitosis, the cut-off value of healthy control (H 2 S:61.5 ppb, CH 3 SH:3.5 ppb), gingivitis (H 2 S:50.0 ppb, CH 3 SH:6 ppb), and periodontitis (H 2 S:62.0 ppb, CH 3 SH:3.5 ppb) were (all p < 0.05). Our results emphasize the close and strong relationship between periodontal disease and halitosis through human clinical evidence based on the high co-occurrence rate of mutual diseases. Additionally, the presence of periodontal disease increased the probability of halitosis by 3.607 times. These results suggest that H 2 S can be used as a biomarker of halitosis in patients with periodontal disease.

The process of hydrodesulfurization is one of the most important heterogeneous catalytic reactions in industry as it helps with reducing global SO x emissions by selectively removing the sulfur contaminants from commercial fuel. In this work, we successfully combine high-pressure scanning tunneling microscopy and reaction modeling using density functional theory to observe the hydrodesulfurization of methanethiol (CH 3 SH) on the Co-substituted S edges of a Co-promoted MoS 2 model catalyst in situ at near-industrial conditions and investigate the plausible reaction pathways. The active sites on the Co-substituted S edges show a time-varying atomic structure influenced by the hydrodesulfurization reaction rate. The involvement of the edge Co site allows for the C-S bond scission to occur at appreciable rates, and is the critical step in the hydrodesulfurization of CH 3 SH. The atomic structures of the S-edge active sites from our reaction models match excellently with those observed in situ in the experiments. Operando scanning tunneling microscopy under near-industrial conditions and density functional theory demonstrate that CH3SH hydrodesulfurization occurs via a new methyl transfer pathway on the Co-substituted S edges of a CoMoS model catalyst.

Oceanic emissions of dimethyl sulfide (CH3SCH3, DMS) have long been recognized to impact aerosol particle composition and size, the concentration of cloud condensation nuclei (CCN), and Earth's radiation balance. The impact of oceanic emissions of methanethiol (CH3SH, MeSH), which is produced by the same oceanic precursor as DMS, on the volatile sulfur budget of the marine atmosphere is largely unconstrained. Here we present direct flux measurements of MeSH oceanic emissions using the eddy covariance (EC) method with a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToFMS) detector and compare them to simultaneous flux measurements of DMS emissions from a coastal ocean site. Campaign mean mixing ratios of DMS and MeSH were 72 ppt (28–90 ppt interquartile range) and 19.1 ppt (7.6–24.5 ppt interquartile range), respectively. Campaign mean emission fluxes of DMS (FDMS) and MeSH (FMeSH) were 1.13 ppt m s−1 (0.53–1.61 ppt m s−1 interquartile range) and 0.21 ppt m s−1 (0.10–0.31 ppt m s−1 interquartile range), respectively. Linear least squares regression of observed MeSH and DMS flux indicates the emissions are highly correlated with each other (R2=0.65) over the course of the campaign, consistent with a shared oceanic source. The campaign mean DMS to MeSH flux ratio (FDMS:FMeSH) was 5.5 ± 3.0, calculated from the ratio of 304 individual coincident measurements of FDMS and FMeSH. Measured FDMS:FMeSH was weakly correlated (R2=0.15) with ocean chlorophyll concentrations, with FDMS:FMeSH reaching a maximum of 10.8 ± 4.4 during a phytoplankton bloom period. No other volatile sulfur compounds were observed by PTR-ToFMS to have a resolvable emission flux above their flux limit of detection or to have a gas-phase mixing ratio consistently above their limit of detection during the study period, suggesting DMS and MeSH are the dominant volatile organic sulfur compounds emitted from the ocean at this site. The impact of this MeSH emission source on atmospheric budgets of sulfur dioxide (SO2) was evaluated by implementing observed emissions in a coupled ocean–atmosphere chemical box model using a newly compiled MeSH oxidation mechanism. Model results suggest that MeSH emissions lead to afternoon instantaneous SO2 production of 2.5 ppt h−1, which results in a 43 % increase in total SO2 production compared to a case where only DMS emissions are considered and accounts for 30% of the instantaneous SO2 production in the marine boundary layer at the mean measured FDMS and FMeSH. This contribution of MeSH to SO2 production is driven by a higher effective yield of SO2 from MeSH oxidation and the shorter oxidation lifetime of MeSH compared to DMS. This large additional source of marine SO2 has not been previously considered in global models of marine sulfur cycling. The field measurements and modeling results presented here demonstrate that MeSH is an important contributor to volatile sulfur budgets in the marine atmosphere and must be measured along with DMS in order to constrain marine sulfur budgets. This large additional source of marine–reduced sulfur from MeSH will contribute to particle formation and growth and CCN abundance in the marine atmosphere, with subsequent impacts on climate.