Aerobic Oxidation Process Research Articles

Microbial acidification by N, S, Fe and Mn oxidation as a key mechanism for deterioration of subsea tunnel sprayed concrete

The deterioration of fibre-reinforced sprayed concrete was studied in the Oslofjord subsea tunnel (Norway). At sites with intrusion of saline groundwater resulting in biofilm growth, the concrete exhibited significant concrete deterioration and steel fibre corrosion. Using amplicon sequencing and shotgun metagenomics, the microbial taxa and surveyed potential microbial mechanisms of concrete degradation at two sites over five years were identified. The concrete beneath the biofilm was investigated with polarised light microscopy, scanning electron microscopy and X-ray diffraction. The oxic environment in the tunnel favoured aerobic oxidation processes in nitrogen, sulfur and metal biogeochemical cycling as evidenced by large abundances of metagenome-assembled genomes (MAGs) with potential for oxidation of nitrogen, sulfur, manganese and iron, observed mild acidification of the concrete, and the presence of manganese- and iron oxides. These results suggest that autotrophic microbial populations involved in the cycling of several elements contributed to the corrosion of steel fibres and acidification causing concrete deterioration.

Synthesis of omega-3 mediated copper (ω-3-Cu) and copper oxide (ω-3-CuO) nanocatalyst dual application of dye decolourization and aerobic oxidation of eco-friendly sustainable approach.

In this study, ω-3-Cu and ω-3-CuO nanocatalysts were investigated for industrial environmental issues. Nowadays, green methodology is very important for addressing industrial environmental issues. In this regard, the current study focuses on ω-3-Cu and ω-3-CuO used for aerobic oxidation and dye decolourization via an eco-friendly approach. The synthesised ω-3-Cu and ω-3-CuO nanocatalysts were characterised using FT-IR, UV, XRD, TEM, GC-MS, 1H and 13C NMR. The results showed that the prepared ω-3-Cu catalyst was almost spherical with forms and sizes typically less than 20nm and the ω-3-CuO nanocatalyst 10nm. The ω-3 Cu and ω-3-CuO nanocatalysts were investigated for the conversion of pentan-2-ol into pentan-2-one, which was observed by GC-MS analysis. The ω-3-CuO nanocatalyst decolourised the Brilliant Blue dye more quickly (100% in 30min) than ω-3-Cu (85% in 60min) and ω-3 (no colour in 60min), and Rhodamine B was not decolourised because our ω-3-Cu and ω-3-CuO nanocatalysts inactivated the rhodamine B dye. The aerobic oxidation process using the ω-3-CuO nanocatalyst as the end product of pentan-2-one resulted in a retention time of 30.33. To the best of our knowledge, ω-3-Cu and ω-3-CuO nanocatalysts have not been documented for their application in decolourisation and aerobic oxidation. By highlighting the potential use for the continued advancement and innovation of ω-3-CuO nanocatalysts in the long-term future, cost-effective and eco-friendly methods for producing reusable ω-3-CuO nanocatalysts have the potential to be applied in advanced technical fields, particularly in the areas of dye decolourisation and aerobic oxidation. Finally, we successfully accomplished these processes using the ω-3-CuO nanocatalyst. The ω-3-CuO nanocatalyst evaporated more quickly than the ω-3-Cu and ω-3-CuO nanocatalyst, without any additional energy. ω-3-CuO is the most effective nanocatalyst for dye decolourization and aerobic oxidation (Dual application). ω-3-CuO is used in textile and pharmaceutical industries.

Regulating Reactive Oxygen Intermediates of Fe–N–C SAzyme via Second‐Shell Coordination for Selective Aerobic Oxidation Reactions

Reactive oxygen species (ROS) regulation for single‐atom nanozymes (SAzymes), e.g., Fe–N–C, is a key scientific issue that determines the activity, selectivity, and stability of aerobic reaction. However, the poor understanding of ROS formation mechanism on SAzymes greatly hampers their wider deployment. Herein, inspired by cytochromes P450 affording bound ROS intermediates in O2 activation, we report Fe–N–C containing the same FeN4 but with tunable second‐shell coordination can effectively regulate ROS production pathways. Remarkably, compared to the control Fe–N–C sample, the second‐shell sulfur functionalized Fe–N–C delivered a·2.4‐fold increase of oxidase‐like activity via the bound Fe=O intermediate. Conversely, free ROS (•O2‐) release was significantly reduced after functionalization, down to only 17% of that observed for Fe–N–C. The detailed characterizations and theoretical calculations revealed that the second‐shell sulfur functionalization significantly altered the electronic structure of FeN4 sites, leading to an increase of electron density at Fermi level. It enhanced the electron transfer from active sites to the key intermediate *OOH, thereby ultimately determining the type of ROS in aerobic oxidation process. The proposed Fe–N–Cs with different second‐shell anion were further applied to three aerobic oxidation reactions with enhanced activity, selectivity, and stability.

Regulating Reactive Oxygen Intermediates of Fe-N-C SAzyme via Second-Shell Coordination for Selective Aerobic Oxidation Reactions.

Reactive oxygen species (ROS) regulation for single-atom nanozymes (SAzymes), e.g., Fe-N-C, is a key scientific issue that determines the activity, selectivity, and stability of aerobic reaction. However, the poor understanding of ROS formation mechanism on SAzymes greatly hampers their wider deployment. Herein, inspired by cytochromes P450 affording bound ROS intermediates in O2 activation, we report Fe-N-C containing the same FeN4 but with tunable second-shell coordination can effectively regulate ROS production pathways. Remarkably, compared to the control Fe-N-C sample, the second-shell sulfur functionalized Fe-N-C delivered a 2.4-fold increase of oxidase-like activity via the bound Fe=O intermediate. Conversely, free ROS (⋅O2 -) release was significantly reduced after functionalization, down to only 17 % of that observed for Fe-N-C. The detailed characterizations and theoretical calculations revealed that the second-shell sulfur functionalization significantly altered the electronic structure of FeN4 sites, leading to an increase of electron density at Fermi level. It enhanced the electron transfer from active sites to the key intermediate *OOH, thereby ultimately determining the type of ROS in aerobic oxidation process. The proposed Fe-N-Cs with different second-shell anion were further applied to three aerobic oxidation reactions with enhanced activity, selectivity, and stability.

Musa acuminata free tepal (MAFT) crop- mediated synthesis of copper oxide nanocatalyst (MAFT-CuO nanocatalyst): Investigation of aerobic oxidation and dye decolourization via eco-friendly approach

Crop development is used to address environmental problems in the industry. Environmental pollutants, particularly humble or toxic chemicals and dyes, are contaminants in industrial wastewater. Recently, green technology has become important for controlling the chemical risks associated with environmental issues. This study focused on valuable crop materials to form green catalysts that can be used to control chemical toxicity in industrial wastewater. In this study, Musa acuminata-free tepal (MAFT) crops and musa were used to mediate the formation of copper nanocatalyst for environmental pollution. The synthesised nanocatalyst was analysed by XPS, XRD, TEM, SEM, FT-IR, GC-EI-MS, and TGA-DSC. The production of Cu–O in the 512 cm−1 peak range was verified by FT-IR analysis. The XRD peaks associated with the cubic crystalline structures of copper (110) and (200) were used to confirm the Musa acuminata-free tepal CuO nanocatalyst. The SEM images of the Cu and CuO nanocatalyst in the Musa acuminata free tepal showed that the particles were almost spherical. The size of the synthesised Musa acuminata free tepal CuO nanocatalyst core-shell nanostructures was identified using HR-TEM. GC-MS investigations also verified the aerobic oxidation of the main alcohol to aldehyde, with a retention time of 30.34. The MAFT was 80 % of CBB G250 dye decolourised at 24 h, and the MAFT-CuO nanocatalyst was decolourised the CBB G250 dye at 80 % in 20 min and aerobic oxidation at the same time (dual application). Furthermore, our nanocatalyst could be effectively recycled without significant loss of catalytic activity, and the use of safe, environmentally benign MAFT-Cu and CuO nanocatalyst is considered a green chemistry approach that helps avoid wastewater treatment. MAFT-Cu and CuO nanocatalyst were successfully synthesised using Musa acuminata free tepal extract assisted by reflux sample preparation system instruments as a new, green, eco-friendly, and fast process for nanocatalyst synthesis. In the past, there have been no reported applications of MAFT-Cu and CuO nanocatalyst for decolourisation and aerobic oxidation. Nevertheless, we were able to accomplish these procedures with the help of CuO and MAFT-Cu nanocatalyst. Therefore, the most effective naturally occurring environmental catalysts for aerobic oxidation processes are MAFT-CuO nanocatalyst. They are non-toxic and environmentally benign, exhibit strong aerobic oxidation catalytic performance, and have long-lasting benefits for water quality. Additionally, they are more recoverable and biodegradable.

Aerobic Oxidative Desulfurization by Supported Polyoxometalate Ionic Liquid Hybrid Materials via Facile Ball Milling.

With the increasingly strict limitations on emission standards of vehicles, deep desulfurization in fuel is indispensable for social development worldwide. In this study, a series of hybrid materials based on SiO2-supported polyoxometalate ionic liquid were successfully prepared via a facile ball milling method and employed as catalysts in the aerobic oxidative desulfurization process. The composition and structure of prepared samples were studied by various techniques, including FT-IR, UV-vis DRS, wide-angle XRD, BET, XPS, and SEM images. The experimental results indicated that the synthesized polyoxometalate ionic liquids were successfully loaded on SiO2 with a highly uniform dispersion. The prepared catalyst (C16PMoV/10SiO2) exhibited good desulfurization activity on different sulfur compounds. Moreover, the oxidation product and active species in the ODS process were respectively investigated via GC-MS and ESR analysis, indicating that the catalyst can activate oxygen to superoxide radicals during the reaction to convert DBT to its corresponding sulfone in the fuel.

FeBr3-catalysed synthesis of 3-aroylimidazo[1,2-a]pyridine and 3,3'-(arylmethylene)bis(2-phenylimidazo[1,2-a]pyridines) derivatives from 2-arylimidazo[1,2-a]pyridines and aromatic aldehydes: an investigation about mechanistic insights.

In a new approach, a series of 3-aroylimidazo[1,2-a]pyridine derivatives were prepared in high yields. This approach revealed the direct Fe-catalyzed functionalization of imidazo[1,2-a]pyridine derivatives with aryl aldehydes via an aerobic oxidative cross-dehydrogenative coupling process. This transformation occurred in the presence of air, and FeBr3 served as a homogeneous Lewis catalyst. O2 was found to be the principal oxidant responsible for the method's success. Interestingly, when these reactions were carried out under an argon atmosphere, 3,3'-(arylmethylene)bis(2-phenylimidazo[1,2-a]pyridines) derivatives were prepared in good yields.

Metabolic reprogramming induced by DCA enhances cisplatin sensitivity through increasing mitochondrial oxidative stress in cholangiocarcinoma.

Background: Cholangiocarcinoma has obvious primary multidrug resistance and is generally resistant to cisplatin and other chemotherapy drugs and high glycolytic levels may be associated with chemotherapy resistance of cholangiocarcinoma cells. Dichloroacetate (DCA) is a specific inhibitor of PDK, which can promote mitochondrial aerobic oxidation process by activating PDH. In the past few years, there have been an increasing number of studies supporting the action of DCA against cancer, which also provided evidence for targeting metabolism to enhance the efficacy of cholangiocarcinoma chemotherapy. Methods: Glucose uptake and lactic acid secretion were used to detect cell metabolism level. Cell apoptosis and cell cycle were detected to confirm cell fate induced by cisplatin combined with DCA. Mito-TEMPO was used to inhibit mtROS to explore the relationship between oxidative stress and cell cycle arrest induced by DCA under cisplatin stress. Finally, PCR array and autophagy inhibitor CQ were used to explore the potential protective mechanism under cell stress. Results: DCA changed the metabolic model from glycolysis to aerobic oxidation in cholangiocarcinoma cells under cisplatin stress. This metabolic reprogramming increased mitochondrial reactive oxygen species (mtROS) levels, which promoted cell cycle arrest, increased the expression of antioxidant genes and activated autophagy. Inhibition of autophagy further increased the synergistic effect of DCA and cisplatin. Conclusion: DCA increased cisplatin sensitivity in cholangiocarcinoma cells via increasing the mitochondria oxidative stress and cell growth inhibition. Synergistic effects of DCA and CQ were observed in cholangiocarcinoma cells, which further increased the cisplatin sensitivity via both metabolic reprogramming and inhibition of the stress response autophagy.

The role of anagostic interactions in the Pd−Superoxo formation in aerobic Pd catalysed C–C coupling reaction: What do DFT computations reveal?

Aerobic oxidative CC coupling catalyzed by dimethyl PdII center (L–[Pd]) bearing tetradentate pyridinophane (N4) ligand L (L = N,N-dimethyl-2,11-diaza[3.3]-(2,6)pyridinophane) has been investigated using density functional theory (DFT) computations. In Pd-catalyzed aerobic oxidation processes, the interaction of dioxygen with PdII center is a crucial step. Computations reveal that the reactant dimethyl PdII complex L–[Pd] has anagostic interactions (4 × Pd···H ∼ 2.60 Å) in total agreement with reported experimental NMR downshift values and these interactions play a significant role in the formation of PdIII–Superoxo intermediate which is less probed. While oxygen approaches the reactant, PdII center becomes PdIII allowing axial amine coordination. This pushes two protons (Csp3–H) away from Pd center weakening the two anagostic interactions. The other two anagostic interactions are intact at long ranges and at closer distances they weaken facilitating Pd–O bonding. The formation of the PdIII center in the PdIII–Superoxo were confirmed by reported EPR measurements. To understand this process, this key step has been modelled. Calculations have been performed with fourteen different density functionals (M06L, B3LYP, PBE0, M06, M11 to name a few) and different basis sets both in gas phase and in solvent medium. It is found that the range separated functionals, particularly M11 functional describe the process accurately and this is attributed to their efficiency of handling electron correlation at different ranges by including different percentage of Hartree-Fock exchange. The role of anagostic interactions M⋯H (M = Ni, Pd and Pt) in metal–superoxo species bearing symmetric and asymmetric substituted N4 ligands have been investigated. These results clearly explain asymmetrically substituted N4 ligands assist the simultaneous creation of M–O bonds at medium ranges and the weakening of bis anagostic (repulsive) M∙∙∙H interactions at short ranges. These findings suggest that intermediate stabilization in CC coupling processes mediated by transition-metal catalysts containing N4 ligands depends critically on the strength of anagostic interactions.

Catalytic Atroposelective Aerobic Oxidation Approaches to Axially Chiral Molecules.

A copper and chiral nitroxide co-catalyzed aerobic enantioselective oxidation process has been developed that allows access to axially chiral molecules. Two complementary atroposelective approaches, oxidative kinetic resolution (OKR) and desymmetrization, were studied using ambient air as the stoichiometric terminal oxidant. OKR of rac-N-arylpyrrole alcohols and rac-biaryl alcohols affords the optically pure compounds with er up to 3.5:96.5 and 5.5:94.5, respectively. Desymmetrization of prochiral diols provides axially chiral biaryl compounds with er up to 99:1.

Palladium Catalyzed Aerobic Oxidative Amination of Alkenes

AbstractAmines are widely applied in the chemical and pharmaceutical industries, and the development of synthetic methods for their preparation is driven by their importance. The amination of alkenes is a direct and efficient method for the construction of amines, of which oxidative amination is more valuable because it can give the desired products with greater functionality and flexibility. In oxidative amination, using molecular oxygen (O2) as a terminal oxidant has promising industrial application prospects. In recent years, the palladium‐catalyzed aerobic oxidation of alkenes has seen significant progress, and its related research has also been extended to the aerobic oxidative amination of alkenes. The corresponding oxidation systems have been developed from early research involving the introduction of cocatalysts to the more recent systems which utilize auxiliary ligands instead of cocatalysts. In this review, the advancements in the palladium‐catalyzed aerobic oxidative amination of monoalkenes and conjugated dienes over the last two decades are discussed, with emphasis on aerobic oxidation process and their associated mechanisms.

Flower-like bismuth oxycarbonate-mediated selective oxidative cleavage of C–C bond in the presence of molecular oxygen

Heterogeneous catalytic and selective C–C bond cleavage is considered as the important way for the production of high valuable compounds from large-molecule-weight feedstock. In this article, a sustainable and efficient aerobic oxidative C–C bond cleavage of lignin models is developed with the bismuth-based solid catalyst. Therein, the flower-like Bi2O2CO3 exhibits a high photocatalytic efficiency in the reaction medium combined of n-butanol and tetramethylammonium bromide. For example, the selective oxidative C–C bond cleavage of 1-phenyl-ethane-1, 2-diol has been successfully carried out, where the substrate conversion and the selectivity of benzaldehyde was 95% and 99%, respectively. The study exhibited that the amount of oxygen vacancies plays a significant role on the photocatalytic selective aerobic oxidative cleavage processes. Moreover, the selective aerobic oxidative C–C bond cleavage of different lignin models was investigated, and all the yields of corresponding products are more than 90% with this photocatalytic system. Furthermore, the used flower-like Bi2O2CO3 can be recycled at least 5 times without the obvious decrease of catalytic activity.

Engineering cytochrome P450s for selective alkene to carbonyl oxidation.

The Wacker-Tsuji oxidation is an important aerobic oxidation process to synthesize ethanal from ethene and methyl ketones from 1-alkenes. Current challenges in aerobic alkene oxidation include selective carbonyl product formation beyond methyl ketones. This includes the regioselective oxidation of the terminal carbon atom of 1-alkenes, the regioselective ketone formation with internal alkenes as well as the enantioselective alkene to carbonyl oxidation. Recently, the potential of high-valent metal-oxo species for direct alkene to carbonyl oxidation was explored as carbonyl product formation is frequently reported as a side reaction of alkene epoxidation by cytochrome P450s. It was shown that such promiscuous P450s can be engineered via directed evolution to perform alkene to carbonyl oxidation reactions with high activity and selectivity. Here, we report a protocol to convert promiscuous P450s into efficient and selective enzymes for Wacker-type alkene oxidation. One round of directed evolution is described in detail, which includes the generation and handling of site-saturation libraries, recombinant protein expression, library screening in a 96-well plate format and the rescreening of variants with beneficial mutations. These protocols might be useful to engineer various P450s for selective alkene to carbonyl oxidation, and to engineer enzymes in general.

The copper-catalyzed oxidative radical process of site selective C–N bond cleavage in twisted amides: batch and continuous-flow chemistry

Copper-superoxo radical activation in twisted amides which mediates the aerobic oxidative process to produce primary amides by selective C–N bond cleavage in batch and continuous-flow method.

Cu‐Oxide Nanoparticles Catalyzed Synthesis of Nitriles and Amides from Alcohols and Ammonia in Presence of Air

AbstractThe synthesis and functionalization of nitrogen‐containing compounds continue to be important due to their wide applications. In particular, the preparation of nitriles and amides applying cost‐effective and green methodologies is of central importance because these products represent valuable fine and bulk chemicals and serve as key precursors and central intermediates in organic synthesis and drug discovery as well as materials. Here, the preparation of nitriles and primary amides from alcohols and ammonia by a heterogeneous Cu‐catalyzed aerobic oxidation process is reported. The optimal catalyst for this synthesis is based on supported copper oxide‐nanoparticles, which are prepared by the impregnation and pyrolysis of simple copper nitrate on carbon. Applying these reusable nanoparticles, various simple, substituted, and functionalized aromatic, heterocyclic, and aliphatic nitriles are synthesized starting from inexpensive and easily accessible alcohols and ammonia in the presence of air. In addition, the synthesis of selected primary amides in a water medium is also performed using these Cu nanoparticles.

Deep aerobic desulfurization of fuels over iron–сontaining zeolite based catalysts

Herein, we present a new approach to the design of the catalysts for aerobic oxidation of sulfur-containing compounds. Iron-containing zeolite-based (ZSM-5, ZSM-12) catalysts were synthesized and successfully tested in oxidation of model mixtures as well as real petroleum fractions. The catalysts were characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV/Vis), temperature programmed desorption of ammonia (NH3-TPD), and low-temperature nitrogen adsorption-desorption. Among these catalysts Fe-ZSM-12 demonstrated the best activity: exhaustive oxidation of dibenzothiophene (DBT) in the presence of this catalyst was achieved in 2 h at 150°C. Influence of the reaction conditions (temperature, amount of catalyst, and time) on the conversion of the model substrate was studied. It was shown that in the presence of Fe-ZSM-12 catalyst activation of molecular oxygen proceeds via formation of superoxide radical. Fe-ZSM-12 exhibited an excellent stability and retained its activity after 10 cycles of oxidation. Under optimal reaction conditions sulfur content in straight-run gasoline fraction was reduced from 807 to 43 ppm, in diesel fraction – from 1898 to 150 ppm. Two-dimensional GC-MS analysis of diesel fraction before and after desulfurization indicates high selectivity of the process. Possibility of sulfur dioxide formation during the aerobic oxidative desulfurization process was studied for the first time. The use of zeolite-based catalysts containing transition metals for aerobic oxidation of sulfur-containing compounds is a promising approach for clean fuel production.

The influence of anaerobic dechlorination on the aerobic degradation of PCBs in e-waste-contaminated soils in an anaerobic-aerobic two-stage treatment

The combination of microbial reductive dechlorination and aerobic oxidation (RD-AO) process was proposed to be a promising strategy for extensive bioremediation of highly chlorinated polychlorinated biphenyls (PCBs). Nonetheless, experimental evidence on the impact of the RD on subsequent AO in anaerobic-aerobic two-stage treatment remains scarce. The present study applied stable-isotope probing (SIP) to explore the RD-AO mediated degradation of PCBs in an e-waste-contaminated soil. The RD-AO treatment resulted in 37.1 % and 48.2 % degradation of PCB180 and PCB9, respectively, while the PCB9 degradation efficiency decreased compared to the sole AO (81.2 %). The inhibition of PCB aerobic degradation might be caused by the alteration of aerobic bacterial community, which was proved by a higher abundance of anaerobic bacteria and a lower abundance of aerobic bacteria being observed in the aerobic stage of RD-AO. Further evidence was obtained using DNA-SIP that the anaerobic stage altered the PCB degraders' community structures and changed three of the five degraders. There were four lineages (Arenimonas, Steroidobacter, Sulfurifustis, and Thermoanaerobacterales) identified as PCB degraders for the first time. Interestingly, three of them were found in RD-AO microcosm, suggesting that anaerobic-aerobic two-stage treatment can recruit novel bacteria involved in PCBs aerobic degradation. The present study provided novel insight into the synergistic integration of anaerobic and aerobic processes for extensive degradation of highly chlorinated PCBs.

Catalytic aerobic oxidation of P(I)/P(III) into P(V) over PdNi10 as a low-cost alternative catalyst rivaling Pd

Chemical oxidation is essential in treating P(I)/P(III)-bearing wastewater, while conventional oxidation processes suffer from low selectivity and high cost induced by oxidant reagents. Herein, a low-cost catalyst PdNi10 was developed to rival the noble metal Pd, which had been known as the only catalyst enabling chemical-free oxidation of P(I)/P(III) into P(V) by ambient O2. The PdNi10 fabricated via optimized method even outperformed Pd in catalytic activity at identical dosage (0.10 g L−1), achieving efficient conversion of 1.00 mM of P(I) into P(V) (>94% in 30 min) with wide applicable pH range from 3.0 to 9.0. The aerobic oxidation of P(I) and P(III) over PdNi10 was confirmed via scavenging experiments to be both dominated by non-radical pathways with apparent activation energies of 44.5 and 21.3 kJ mol−1, respectively. Interestingly, the individual roles of Ni components of PdNi10 in the catalytic oxidation were found negligible. The H2O-methanol binary solvent experiment suggested that H2O mediated the catalytic reaction and the interfacial OH groups as a result of H2O dissociation served as the main reactive oxidant species for P(I)/P(III) oxidation. Furthermore, synergistic mechanism was proposed for the Ni and Pd sites with favorable roles in the essential reaction steps of dehydrogenation and hydroxylation, respectively. This study is believed to advance the treatment strategy of P(I)/P(III)-rich wastewater and to shed new light on the development of low-cost catalysts enabling chemical-free aerobic oxidation processes under facile condition.

Nitrogen input promotes denitrifying methanotrophs’ abundance and contribution to methane emission reduction in coastal wetland and paddy soil

Denitrifying anaerobic methane oxidation (DAMO) microorganisms, using nitrate/nitrite to oxidize methane, have been proved to be an important microbial methane sink in natural habitats. Increasing nitrogen deposit around the globe brings increased availability of substrates for these microorganisms. However, how elevated nitrogen level affects denitrifying methanotrophs has not been elucidated. In this study, sediment/soil samples from coastal wetland with continuous nitrogen input and paddy field with periodic nitrogen input were collected to investigate the influence of nitrogen input on the abundance and activity of denitrifying methanotrophs. The results indicated that nitrogen input significantly promoted DAMO microorganisms’ abundance and contribution to methane emission reduction. In the coastal wetland, the contribution rate of DAMO process to methane removal increased from 12.1% to 33.5% along with continuously elevated nitrogen level in the 3-year tracking study. In the paddy field, the DAMO process accounted for 71.9% of total methane removal when nitrogen fertilizer was applied during the growing season, exceeding the aerobic methane oxidation process. This work would help us better understand the microbial methane cycle and reduce uncertainties in the estimations of the global methane emission.

Two Novel Thermotolerant Methane Oxidizers from a Tropical Natural Gas Field in Bangladesh

Aerobic thermotolerant methane oxidizers utilize methane as a sole carbon and energy source, and predominantly they are associated with the phylum Proteobacteria. Here we present two further new strains (HGS-45: coccusshaped and HGF-47: rod-shaped and vibrioid) of thermotolerant obligate proteobacterial methanotrophic bacteria, which were isolated from an abandoned tropical natural gas field wet soil sample in the northeast of Bangladesh. Strains are Gram-negative, nonmotile, and capable of growth on methane and methanol as their energy sources. Isolates are thermotolerant and could grow up to 52oC, optimally at 42oC, but show no growth at 55 or 15oC. Based on 16S rRNA gene sequence analyses and phylogenetically, HGS-45 is most closely related to the obligate Type Ib methanotroph Methylococcus capsulatus of the family Methylococcaceae, whereas HGF-47 is affiliated to Type IIa methanotroph Methylocystis sp. of the family Methylocystaceae and possesses Type II intracytoplasmic membrane (ICM) systems. Genes of particulate methane monooxygenase (pMMO) and the methanol dehydrogenase (MDH) were detected by PCR. Southern-blot analyses of genomic DNA from both strains were positive, implying the aerobic biological oxidation process from methane to methanol by the pMMO. Each strain presumably represents a novel species. Furthermore, both strains will increase our knowledge of thermotolerant methanotrophic proteobacterial diversity, cohabitation, and their participation to global carbon cycles as well as signifying biological methane sinks in the terrestrial natural gas field ecosystems. Bangladesh J Microbiol, Volume 38, Number 2, December 2021, pp 63-71