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1.
Enhancing mainstream nitrogen removal by employing nitrate/nitrite-dependent anaerobic methane oxidation processes.
Liu, T, Hu, S, Guo, J
Critical reviews in biotechnology. 2019;(5):732-745
Abstract
Due to serious eutrophication in water bodies, nitrogen removal has become a critical stage for wastewater treatment plants (WWTPs) over past decades. Conventional biological nitrogen removal processes are based on nitrification and denitrification (N/DN), and are suffering from several major drawbacks, including substantial aeration consumption, high fugitive greenhouse gas emissions, a requirement for external carbon sources, excessive sludge production and low energy recovery efficiency, and thus unable to satisfy the escalating public needs. Recently, the discovery of anaerobic ammonium oxidation (anammox) bacteria has promoted an update of conventional N/DN-based processes to autotrophic nitrogen removal. However, the application of anammox to treat domestic wastewater has been hindered mainly by unsatisfactory effluent quality with nitrogen removal efficiency below 80%. The discovery of nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) during the last decade has provided new opportunities to remove this barrier and to achieve a robust system with high-level nitrogen removal from municipal wastewater, by utilizing methane as an alternative carbon source. In the present review, opportunities and challenges for nitrate/nitrite-dependent anaerobic methane oxidation are discussed. Particularly, the prospective technologies driven by the cooperation of anammox and n-DAMO microorganisms are put forward based on previous experimental and modeling studies. Finally, a novel WWTP system acting as an energy exporter is delineated.
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2.
Influence of surfactants on anaerobic digestion of waste activated sludge: acid and methane production and pollution removal.
He, Q, Xu, P, Zhang, C, Zeng, G, Liu, Z, Wang, D, Tang, W, Dong, H, Tan, X, Duan, A
Critical reviews in biotechnology. 2019;(5):746-757
Abstract
The objective of this study is to summarize the effects of surfactants on anaerobic digestion (AD) of waste activated sludge (WAS). The increasing amount of WAS has caused serious environmental problems. Anaerobic digestion, as the main treatment for WAS containing three stages (i.e. hydrolysis, acidogenesis, and methanogenesis), has been widely investigated. Surfactant addition has been demonstrated to improve the efficiency of AD. Surfactant, as an amphipathic substance, can enhance the efficiency of hydrolysis by separating large sludge and releasing the encapsulated hydrolase, providing more substance for subsequent acidogenesis. Afterwards, the short chain fatty acids (SCFAs), as the major product, have been produced. Previous investigations revealed that surfactant could affect the transformation of SCFA. They changed the types of acidification products by promoting changes in microbial activity and in the ratio of carbon to nitrogen (C/N), especially the ratio of acetic and propionic acid, which were applied for either the removal of nutrient or the production of polyhydroxyalkanoate (PHA). In addition, the activity of microorganisms can be affected by surfactant, which mainly leads to the activity changes of methanogens. Besides, the solubilization of surfactant will promote the solubility of contaminants in sludge, such as organic contaminants and heavy metals, by increasing the bioavailability or desorbing of the sludge.
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3.
Genome scale metabolic modeling reveals the metabolic potential of three Type II methanotrophs of the genus Methylocystis.
Bordel, S, Rodríguez, Y, Hakobyan, A, Rodríguez, E, Lebrero, R, Muñoz, R
Metabolic engineering. 2019;:191-199
Abstract
Genome Scale Metabolic Models (GSMMs) of the recently sequenced Methylocystis hirsuta and two other methanotrophs from the genus Methylocystis have been reconstructed. These organisms are Type II methanotrophs with the ability of accumulating Polyhydroxyalkanoates under nutrient limiting conditions. For the first time, GSMMs have been reconstructed for Type II methanotrophs. These models, combined with experimental biomass and PHB yields of Methylocystis hirsuta, allowed elucidating the methane oxidation mechanism by the enzyme pMMO (particulate methane monooxygenase) in these organisms. In contrast to Type I methanotrophs, which use the "direct coupling mechanism", Type II methanotrophs appear to use the so called "redox arm mechanism". The utilization of the "redox arm mechanism", which involves the coupling between methane oxidation and complex I of the respiratory chain, was confirmed by inhibition of complex I with catechol. Utilization of the "redox arm" mechanism leads to lower biomass yields on methane compared to Type I methanotrophs. However, the ability of Type II methanotrophs to redirect high metabolic carbon fluxes towards acetoacetyl-CoA under nitrogen limiting conditions makes these organisms promising platforms for metabolic engineering.
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4.
Metagenomic assessment of the microbial community and methanogenic pathways in biosolids from a municipal wastewater treatment plant in Medellín, Colombia.
Bedoya, K, Coltell, O, Cabarcas, F, Alzate, JF
The Science of the total environment. 2019;:572-581
Abstract
Abundance and diversity of microbial communities in biosolids are variable and poorly studied in the tropics, and it is known that rainfall is one of the events that could affect the phylogenetic and functional microbial structure. In the present study, using NGS technics, we studied the microbial diversity as well as the methanogenesis pathway in one of the largest WWTP in Colombia. Besides, we sampled and analyzed biosolids from rainy season and dry season. Phylogenetic classification showed a predominance of bacteria in both samples and difference in the dominant groups depending on the rainfall season. Whereas Pseudomonas was the dominant bacteria in the dry season, Coprothermobacter was in the rainy season. Archaea abundance was higher in the rainy season (11.5%) doubling dry season proportion. The bioreactor biogas production and total solids content showed similar results between rainy and dry season at the sampling dates. The most abundant Archaea related with methanogenesis was Methanosaeta, which is a methanogenic microorganism that exclusively uses acetate to produce methane. Moreover, annotation of the methanogenic pathway in the metagenome showed abundance in genes encoding Acetyl-CoA synthetases (ACSS), an enzyme that catalyzes acetate activation. Our results suggest that the microbial diversity was stable among the two time points tested, rainy season and dry season; and, although there were changes in the microbial abundance of dominant bacterial species, anaerobic digester performance is not affected.
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5.
Methanotrophy - Environmental, Industrial and Medical Applications.
Semrau, JD, DiSpirito, AA
Current issues in molecular biology. 2019;:1-22
Abstract
Aerobic methanotrophs are an intriguing group of microbes with the singular ability to consume methane as their sole source of carbon and energy. As such, methanotrophs are receiving increased attention to control methane emissions to limit future climate change. Methanotrophs have a wide range of other applications, including pollutant remediation and methane valorization (e.g. conversion of methane to protein, bioplastics, and biodiesel amongst other products). Methanotrophs also produce a novel copper-binding compound, methanobactin, that has significant potential for the treatment of copper-related human pathologies. Here we provide an overview of aerobic methanotrophy, describe current and future applications of these unique microbes, as well as discuss various strategies one can consider to better realize the opportunities these microbes present.
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6.
Physiology and Distribution of Archaeal Methanotrophs That Couple Anaerobic Oxidation of Methane with Sulfate Reduction.
Bhattarai, S, Cassarini, C, Lens, PNL
Microbiology and molecular biology reviews : MMBR. 2019;(3)
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Abstract
In marine anaerobic environments, methane is oxidized where sulfate-rich seawater meets biogenic or thermogenic methane. In those niches, a few phylogenetically distinct microbial types, i.e., anaerobic methanotrophs (ANME), are able to grow through anaerobic oxidation of methane (AOM). Due to the relevance of methane in the global carbon cycle, ANME have drawn the attention of a broad scientific community for 4 decades. This review presents and discusses the microbiology and physiology of ANME up to the recent discoveries, revealing novel physiological types of anaerobic methane oxidizers which challenge the view of obligate syntrophy for AOM. An overview of the drivers shaping the distribution of ANME in different marine habitats, from cold seep sediments to hydrothermal vents, is given. Multivariate analyses of the abundance of ANME in various habitats identify a distribution of distinct ANME types driven by the mode of methane transport. Intriguingly, ANME have not yet been cultivated in pure culture, despite intense attempts. Further advances in understanding this microbial process are hampered by insufficient amounts of enriched cultures. This review discusses the advantages, limitations, and potential improvements for ANME laboratory-based cultivation systems.
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7.
Decreased Snow Cover Stimulates Under-Ice Primary Producers but Impairs Methanotrophic Capacity.
Garcia, SL, Szekely, AJ, Bergvall, C, Schattenhofer, M, Peura, S
mSphere. 2019;(1)
Abstract
Climate change scenarios anticipate decreased spring snow cover in boreal and subarctic regions. Forest lakes are abundant in these regions and substantial contributors of methane emissions. To investigate the effect of reduced snow cover, we experimentally removed snow from an anoxic frozen lake. We observed that the removal of snow increased light penetration through the ice, increasing water temperature and modifying microbial composition in the different depths. Chlorophyll a and b concentrations increased in the upper water column, suggesting activation of algal primary producers. At the same time, Chlorobiaceae, one of the key photosynthetic bacterial families in anoxic lakes, shifted to lower depths. Moreover, a decrease in the relative abundance of methanotrophs within the bacterial family Methylococcaceae was detected, concurrent with an increase in methane concentration in the water column. These results indicate that decreased snow cover impacts both primary production and methane production and/or consumption, which may ultimately lead to increased methane emissions after spring ice off.IMPORTANCE Small lakes are an important source of greenhouse gases in the boreal zone. These lakes are severely impacted by the winter season, when ice and snow cover obstruct gas exchange between the lake and the atmosphere and diminish light availability in the water column. Currently, climate change is resulting in reduced spring snow cover. A short-term removal of the snow from the ice stimulated algal primary producers and subsequently heterotrophic bacteria. Concurrently, the relative abundance of methanotrophic bacteria decreased and methane concentrations increased. Our results increase the general knowledge of microbial life under ice and, specifically, the understanding of the potential impact of climate change on boreal lakes.
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8.
Methane production and emissions in trees and forests.
Covey, KR, Megonigal, JP
The New phytologist. 2019;(1):35-51
Abstract
Contents Summary 35 I. Introduction 36 II. Tree CH4 fluxes 36 III. Tree emissions of soil-produced CH4 40 IV. Tree-produced CH4 42 V. Trees in forest CH4 budgets 44 VI. Conclusions 46 Acknowledgements 48 Author contributions 48 References 48 SUMMARY Forest ecosystem methane (CH4 ) research has focused on soils, but trees are also important sources and sinks in forest CH4 budgets. Living and dead trees transport and emit CH4 produced in soils; living trees and dead wood emit CH4 produced inside trees by microorganisms; and trees produce CH4 through an abiotic photochemical process. Here, we review the state of the science on the production, consumption, transport, and emission of CH4 by living and dead trees, and the spatial and temporal dynamics of these processes across hydrologic gradients inclusive of wetland and upland ecosystems. Emerging research demonstrates that tree CH4 emissions can significantly increase the source strength of wetland forests, and modestly decrease the sink strength of upland forests. Scaling from stem or leaf measurements to trees or forests is limited by knowledge of the mechanisms by which trees transport soil-produced CH4 , microbial processes produce and oxidize CH4 inside trees, a lack of mechanistic models, the diffuse nature of forest CH4 fluxes, complex overlap between sources and sinks, and extreme variation across individuals. Understanding the complex processes that regulate CH4 source-sink dynamics in trees and forests requires cross-disciplinary research and new conceptual models that transcend the traditional binary classification of wetland vs upland forest.
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Metal-dependent anaerobic methane oxidation in marine sediment: Insights from marine settings and other systems.
Liang, L, Wang, Y, Sivan, O, Wang, F
Science China. Life sciences. 2019;(10):1287-1295
Abstract
Anaerobic oxidation of methane (AOM) plays a crucial role in controlling global methane emission. This is a microbial process that relies on the reduction of external electron acceptors such as sulfate, nitrate/nitrite, and transient metal ions. In marine settings, the dominant electron acceptor for AOM is sulfate, while other known electron acceptors are transient metal ions such as iron and manganese oxides. Despite the AOM process coupled with sulfate reduction being relatively well characterized, researches on metal-dependent AOM process are few, and no microorganism has to date been identified as being responsible for this reaction in natural marine environments. In this review, geochemical evidences of metal-dependent AOM from sediment cores in various marine environments are summarized. Studies have showed that iron and manganese are reduced in accordance with methane oxidation in seeps or diffusive profiles below the methanogenesis zone. The potential biochemical basis and mechanisms for metal-dependent AOM processes are here presented and discussed. Future research will shed light on the microbes involved in this process and also on the molecular basis of the electron transfer between these microbes and metals in natural marine environments.
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Growth kinetics of Candidatus 'Methanoperedens nitroreducens' enriched in a laboratory reactor.
Lu, P, Liu, T, Ni, BJ, Guo, J, Yuan, Z, Hu, S
The Science of the total environment. 2019;:442-450
Abstract
Recently it has been shown that Candidatus 'Methanoperedens nitroreducens', an anaerobic methanotrophic archaea (ANME), can reduce nitrate to nitrite using electrons derived from anaerobic oxidation of methane. In this study, the growth kinetics of 'M. nitroreducens' enriched in a laboratory reactor were studied. In the experimental concentration range (up to 16 mg CH4 L-1), anaerobic oxidation of methane by 'M. nitroreducens' was found to comply with first order kinetic model with a rate constant of 0.019 ± 0.006 h-1 and a biomass-specific rate constant of 0.04-0.14 L h-1 g-1VSS. Meanwhile, the nitrate reduction to nitrite was well described by the Monod-type kinetic model with an affinity constant for nitrate of 2.1 ± 0.4 mg N L-1, which is slightly higher than, but comparable to, that of most known denitrifying bacteria. This is the first time that the growth kinetics of 'M. nitroreducens' have been experimentally studied. The applicability of the kinetic model reported herein to this organism or similar organisms in natural or engineering systems requires further investigation.