Methanol Production by "Methylacidiphilum fumariolicum" SolV under Different Growth Conditions

Emissions of volatile organic compounds from aboveground and belowground parts of rapeseed (Brassica napus L.) and tomato (Solanum lycopersicum L.)

Root systems represent a source of Volatile Organic Compounds (VOCs) that may significantly contribute to the atmospheric VOC emissions from agroecosystems and shape soil microbial activity. To gain deeper insights into the role of roots in the VOC emissions from crops, we developed a dynamic chamber with isolated aboveground and belowground compartments, allowing for simultaneous measurements of VOC fluxes from both compartments in controlled conditions. We continuously monitored VOC emissions from intact plants of rapeseed (Brassica napus L.) and tomato (Solanum lycopersicum L.) i) over 24 h when plants were rooted in soil, and ii) over 6 h following soil removal. The measurements were performed using a highly sensitive Proton Transfer Reaction - Time of Flight - Mass Spectrometer and a Thermic Desorption- Gas Chromatography - Mass Spectrometer. Net VOC emissions measured at the soil surface represented <5 % of the aboveground emissions and were higher during the day than at night. However, when soil was removed, belowground VOC emissions became up to two times higher than aboveground emissions. This large increase in VOC emissions from roots observed after soil removal was almost exclusively due to methanol emissions. Differences in VOC composition between plant species were also detected with and without soil: rapeseed emitted more sulphurous and nitrogenous compounds and tomato more mono- and poly-unsaturated hydrocarbons. Our results suggest that roots may be a largely underestimated VOC source and that the soil is a strong sink for root-borne methanol. Root VOC emissions should be considered when agricultural practices involve roots excavation.

Microbial communities in petroleum refinery effluents and their complex functions

Petroleum refinery effluents (PRE) are a significant cause of pollution. It contains toxic compounds such as total petroleum hydrocarbons (TPH), and polycyclic aromatic hydrocarbons (PAHs), as well as heavy metals. They show a huge threat facing the aquaculture habitats, human health, and the environment if they are not treated before discharging into the environment. Physical and chemical procedures are used to treat hydrocarbon pollution in PRE, but these techniques often result in the formation of hazardous by-products during the remediation process. However, PRE contains various microbial communities, including bacteria, yeast, microalgae, and fungi. The bioremediation and biodegradation of oil contaminants are the primary functions of these microbial communities. However, these microorganisms can perform various additional functions including but not limited to heavy metals removal, production of biosurfactants, and nitrogen fixation. This review contributes to the comprehension of natural microbial communities and their complex functions in petroleum refinery effluents. Understanding microbial communities would facilitate the advancement of innovative biotechnology aimed at treating PRE, improving bioremediation processes, and potentially transforming PRE into valuable bio-products. Moreover, it assists in determining the most effective bioaugmentation strategy to enhance biodegradation and bioremediation in PRE. The review highlights the potential for sustainable green approaches using microbial communities to replace toxic chemical therapies and expensive physical treatments in the future.

Interaction between methanotrophy and gastrointestinal nematodes infection on the rumen microbiome of lambs

Complex cross-talk occurs between gastrointestinal nematodes and gut symbiotic microbiota, with consequences for animal metabolism. To investigate the connection between methane production and endoparasites, this study evaluated the effect of mixed infection with Haemonchus contortus and Trichostrongylus colubriformis on methanogenic and methanotrophic community in rumen microbiota of lambs using shotgun metagenomic and real-time quantitative PCR (qPCR). The rumen content was collected from six Santa Inês lambs, (7 months old) before and after 42 days infection by esophageal tube. The metagenomic analysis showed that the infection affected the microbial community structure leading to decreased abundance of methanotrophs bacteria, i.e. α-proteobacteria and β-proteobacteria, anaerobic methanotrophic archaea (ANME), protozoa, sulfate-reducing bacteria, syntrophic bacteria with methanogens, geobacter, and genes related to pyruvate, fatty acid, nitrogen, and sulfur metabolisms, ribulose monophosphate cycle, and Entner-Doudoroff Pathway. Additionally, the abundance of methanogenic archaea and the mcrA gene did not change. The co-occurrence networks enabled us to identify the interactions between each taxon in microbial communities and to determine the reshaping of rumen microbiome associations by gastrointestinal nematode infection. Besides, the correlation between ANMEs was lower in the animal's postinfection. Our findings suggest that gastrointestinal parasites potentially lead to decreased methanotrophic metabolism-related microorganisms and genes.

Encapsulation of Methanotrophs within a Polymeric Matrix Containing Copper- and Iron-Based Nanoparticles to Enhance Methanol Production from a Simulated Biogas

The production of renewable energy or biochemicals is gaining more attention to minimize the emissions of greenhouse gases such as methane (CH4) and carbon dioxide for sustainable development. In the present study, the influence of copper (Cu)- and iron (Fe)-based nanoparticles (NPs), such as Cu, Fe3O4, and CuFe2O4, was evaluated during the growth of methanotrophs for inoculum preparation and on the development of a polymeric-matrix-based encapsulation system to enhance methanol production from simulated biogas (CH4 and CO2). The use of simulated biogas feed and the presence of NP-derived inoculums produce a remarkable enhancement in methanol production up to 149% and 167% for Methyloferula stellata and Methylocystis bryophila free-cells-based bioconversion, respectively, compared with the use of pure CH4 as a control feed during the growth stage. Furthermore, these methanotrophs encapsulated within a polymeric matrix and NPs-based systems exhibited high methanol production of up to 156%, with a maximum methanol accumulation of 12.8 mmol/L over free cells. Furthermore, after encapsulation, the methanotrophs improved the stability of residual methanol production and retained up to 62.5-fold higher production potential than free cells under repeated batch reusability of 10 cycles. In the presence of CH4 vectors, methanol production by M. bryophila improved up to 16.4 mmol/L and retained 20% higher recycling stability for methanol production in paraffin oil. These findings suggest that Cu and Fe NPs can be beneficially employed with a polymeric matrix to encapsulate methanotrophs and improve methanol production.

Biomethanol production from renewable resources: a sustainable approach

The abundant availability of various kinds of biomass and their use as feedstock for the production of gaseous and liquid biofuels has been considered a viable, eco-friendly, and sustainable mode of energy generation. Gaseous fuels like biogas and liquid fuels, e.g., bioethanol, biodiesel, and biomethanol derived from biological sources, have been theorized to produce numerous industrially relevant organic compounds replacing the traditional practice of employing fossil fuels as a raw material. Among the biofuels explored, biomethanol has shown promising potential to be a future product addressing multifactorial issues concerning sustainable energy and associated process developments. The presented mini-review has explored the importance and application of biomethanol as a value-added product. The biomethanol production process was well reviewed by focusing on different thermochemical and biochemical conversion processes. Syngas and biogas have been acknowledged as potential resources for biomethanol synthesis. The emphasis on biochemical processes is laid on the principal metabolic pathways and enzymatic machinery involved or used by microbial physiology to convert feedstock into biomethanol under normal temperature and pressure conditions. The advantage of minimizing the cost of production by utilizing suggested modifications to the overall process of biomethanol production that involves metabolic and genetic engineering in microbial strains used in the production process has been delineated. The challenges that exist in our current knowledge domain, impeding large-scale commercial production potential of biomethanol at a cost-effective rate, and strategies to overcome them along with its future scenarios have also been pointed out.

Integration of biogas derived from dark fermentation and anaerobic digestion of biowaste to enhance methanol production by methanotrophs

Biowaste-derived sugars or greenhouse gases, such as methane (CH₄) and carbon dioxide (CO₂), can be used to generate eco-friendly biofuels, such as hydrogen (H₂) or methanol. In the present study, enzyme-based rice straw (RS) hydrolysate was used to produce dark-fermentative (DF) biogas (H₂ and CO₂), which was subsequently integrated with biogas (CH₄ and CO₂) derived from anaerobic digestion (AD) to generate methanol via methanotrophs. First, DF of RS hydrolysate yielded 2.82 mol of H₂/mol of hexose. Second, the integration of biogas derived from DF and AD in the presence of CH₄ vectors yielded 13.8 mmol/L of methanol via methanotrophs. Moreover, under the repeated batch mode, 64.6 mmol/L of methanol was produced. This is the first report on the integration of biogas derived from AD and DF of biowaste to produce biomethanol. These findings may facilitate the development of a sustainable biowaste-based circular economy for producing biofuels.

Synthetic design of methanotroph co-cultures and their immobilization within polymers containing magnetic nanoparticles to enhance methanol production from wheat straw-based biogas

In this study, various methanotroph co-cultures were designed to enhance methanol production from biogas produced through the anaerobic digestion of wheat straw (WS). Furthermore, whole-cell immobilization was performed using magnetic nanoparticle (MNP)-loaded polymers to develop an efficient bioprocess. The anaerobic digestion of WS by cattle dung yielded 219 L/kg of total solids reduced. Methanol produced was 5.08 and 6.39 mmol/L by pure- and co-cultures from biogas, respectively. The optimization of process parameters enhanced methanol production to 6.82 mmol/L by co-culturing Mithylosinus sporium and Methylocella tundrae. The immobilized co-culture within the MNP-doped polymers exhibited much higher cumulative methanol of up to 70.74 mmol/L than the production of 22.34 mmol/L by free cells after ten cycles of reuse. This study suggests that MNP-doped polymer-based immobilization of methanotrophs is a unique approach for producing renewable fuels from biomass-derived biogas, a greenhouse gas.

Employing methylotrophs for a green economy: one-carbon to fuel them all and through metabolism redesign them

Microbial platforms are currently being optimized to revolutionize industrial energy production while mitigating shortages of global resources and food supplies. Here, we address recent advances to develop bacterial methylotrophic platforms as promising platforms enabling the reuse of products and materials (at their highest value) while reducing waste and pollution.

Biomolecules Production from Greenhouse Gases by Methanotrophs

Harmful effects on living organisms and the environment are on the rise due to a significant increase in greenhouse gas (GHG) emissions through human activities. Therefore, various research initiatives have been carried out in several directions in relation to the utilization of GHGs via physicochemical or biological routes. An environmentally friendly approach to reduce the burden of significant emissions and their harmful effects is the bioconversion of GHGs, including methane (CH4) and carbon dioxide (CO2), into value-added products. Methanotrophs have enormous potential for the efficient biotransformation of CH4 to various bioactive molecules, including biofuels, polyhydroxyalkanoates, and fatty acids. This review highlights the recent developments in methanotroph-based systems for methanol production from GHGs and proposes future perspectives to improve process sustainability via biorefinery approaches.

Recent trends in methane to bioproduct conversion by methanotrophs

Methane is an abundant and low-cost gas with high global warming potential and its use as a feedstock can help mitigate climate change. Variety of valuable products can be produced from methane by methanotrophs in gas fermentation processes. By using methane as a sole carbon source, methanotrophic bacteria can produce bioplastics, biofuels, feed additives, ectoine and variety of other high-value chemical compounds. A lot of studies have been conducted through the years for natural methanotrophs and engineered strains as well as methanotrophic consortia. These have focused on increasing yields of native products as well as proof of concept for the synthesis of new range of chemicals by metabolic engineering. This review shows trends in the research on key methanotrophic bioproducts since 2015. Despite certain limitations of the known production strategies that makes commercialization of methane-based products challenging, there is currently much attention placed on the promising further development.

Verrucomicrobial methanotrophs grow on diverse C3 compounds and use a homolog of particulate methane monooxygenase to oxidize acetone

Short-chain alkanes (SCA; C2-C4) emitted from geological sources contribute to photochemical pollution and ozone production in the atmosphere. Microorganisms that oxidize SCA and thereby mitigate their release from geothermal environments have rarely been studied. In this study, propane-oxidizing cultures could not be grown from acidic geothermal samples by enrichment on propane alone, but instead required methane addition, indicating that propane was co-oxidized by methanotrophs. “Methylacidiphilum” isolates from these enrichments did not grow on propane as a sole energy source but unexpectedly did grow on C3 compounds such as 2-propanol, acetone, and acetol. A gene cluster encoding the pathway of 2-propanol oxidation to pyruvate via acetol was upregulated during growth on 2-propanol. Surprisingly, this cluster included one of three genomic operons (pmoCAB3) encoding particulate methane monooxygenase (PMO), and several physiological tests indicated that the encoded PMO3 enzyme mediates the oxidation of acetone to acetol. Acetone-grown resting cells oxidized acetone and butanone but not methane or propane, implicating a strict substrate specificity of PMO3 to ketones instead of alkanes. Another PMO-encoding operon, pmoCAB2, was induced only in methane-grown cells, and the encoded PMO2 could be responsible for co-metabolic oxidation of propane to 2-propanol. In nature, propane probably serves primarily as a supplemental growth substrate for these bacteria when growing on methane.

Methanotrophs: Discoveries, Environmental Relevance, and a Perspective on Current and Future Applications

Methane is the final product of the anaerobic decomposition of organic matter. The conversion of organic matter to methane (methanogenesis) as a mechanism for energy conservation is exclusively attributed to the archaeal domain. Methane is oxidized by methanotrophic microorganisms using oxygen or alternative terminal electron acceptors. Aerobic methanotrophic bacteria belong to the phyla Proteobacteria and Verrucomicrobia, while anaerobic methane oxidation is also mediated by more recently discovered anaerobic methanotrophs with representatives in both the bacteria and the archaea domains. The anaerobic oxidation of methane is coupled to the reduction of nitrate, nitrite, iron, manganese, sulfate, and organic electron acceptors (e.g., humic substances) as terminal electron acceptors. This review highlights the relevance of methanotrophy in natural and anthropogenically influenced ecosystems, emphasizing the environmental conditions, distribution, function, co-existence, interactions, and the availability of electron acceptors that likely play a key role in regulating their function. A systematic overview of key aspects of ecology, physiology, metabolism, and genomics is crucial to understand the contribution of methanotrophs in the mitigation of methane efflux to the atmosphere. We give significance to the processes under microaerophilic and anaerobic conditions for both aerobic and anaerobic methane oxidizers. In the context of anthropogenically influenced ecosystems, we emphasize the current and potential future applications of methanotrophs from two different angles, namely methane mitigation in wastewater treatment through the application of anaerobic methanotrophs, and the biotechnological applications of aerobic methanotrophs in resource recovery from methane waste streams. Finally, we identify knowledge gaps that may lead to opportunities to harness further the biotechnological benefits of methanotrophs in methane mitigation and for the production of valuable bioproducts enabling a bio-based and circular economy.

Laboratory scale bioreactor designs in the processes of methane bioconversion: Mini-review

Global methane emissions have been steadily increasing over the past few decades, exerting a negative effect on the environment. Biogas from landfills and sewage treatment plants is the main anthropogenic source of methane. This makes methane bioconversion one of the priority areas of biotechnology. This process involves the production of biochemical compounds from non-food sources through microbiological synthesis. Methanotrophic bacteria are a promising tool for methane bioconversion due to their ability to use this greenhouse gas and to produce protein-rich biomass, as well as a broad range of useful organic compounds. Currently, methane is used not only to produce biomass and chemical compounds, but also to increase the efficiency of water and solid waste treatment. However, the use of gaseous substrates in biotechnological processes is associated with some difficulties. The low solubility of methane in water is one of the major problems. Different approaches have been involved to encounter these challenges, including different bioreactor and gas distribution designs, solid carriers and bulk sorbents, as well as varying air/oxygen supply, the ratio of volumetric flow rate of gas mixture to its consumption rate, etc. The aim of this review was to summarize the current data on different bioreactor designs and the aspects of their applications for methane bioconversion and wastewater treatment. The bioreactors used in these processes must meet a number of requirements such as low methane emission, improved gas exchange surface, and controlled substrate supply to the reaction zone.

Verrucomicrobial methanotrophs: ecophysiology of metabolically versatile acidophiles

Methanotrophs are an important group of microorganisms that counteract methane emissions to the atmosphere. Methane-oxidising bacteria of the Alpha- and Gammaproteobacteria have been studied for over a century, while methanotrophs of the phylum Verrucomicrobia are a more recent discovery. Verrucomicrobial methanotrophs are extremophiles that live in very acidic geothermal ecosystems. Currently, more than a dozen strains have been isolated, belonging to the genera Methylacidiphilum and Methylacidimicrobium. Initially, these methanotrophs were thought to be metabolically confined. However, genomic analyses and physiological and biochemical experiments over the past years revealed that verrucomicrobial methanotrophs, as well as proteobacterial methanotrophs, are much more metabolically versatile than previously assumed. Several inorganic gases and other molecules present in acidic geothermal ecosystems can be utilised, such as methane, hydrogen gas, carbon dioxide, ammonium, nitrogen gas and perhaps also hydrogen sulfide. Verrucomicrobial methanotrophs could therefore represent key players in multiple volcanic nutrient cycles and in the mitigation of greenhouse gas emissions from geothermal ecosystems. Here, we summarise the current knowledge on verrucomicrobial methanotrophs with respect to their metabolic versatility and discuss the factors that determine their diversity in their natural environment. In addition, key metabolic, morphological and ecological characteristics of verrucomicrobial and proteobacterial methanotrophs are reviewed.