CH4 production at moderate H2/CO2 pressures insights on the use of anaerobic granular sludge as biocatalyst

Introduction: The continuous increase in energy consumption and the intensive use of fossil fuels, lead to the emission of greenhouse gases (GHG) and, in particular, to an increase in the concentration of CO2 in the atmosphere. In this context, the improvement in global awareness and the demand for sustainable technologies and products strongly contribute to laid plans to combat climate change. CO2-to-CH4 conversion represents a cutting-edge solution for CO2 capture and use, contributing to the reduction of GHG emission. Catalytic conversion of CO2-to-CH4 have been investigated, however, the high cost associated to the catalysts employed limits their use on a large scale. Biological CO2 methanation can overcome the significant technical and economic challenges of catalytic CO2 methanation. The biological production of CH4 using CO2-rich gases together with H2 is a promising strategy for the production of bioproducts. Hydrogenotrophic methanogens have a crucial role on the direct conversion of CO2+H2 into CH4, hence the importance to study the specific hydrogenotrophic methanogenic activity (SHMA). Methodology: In this work, the effect of initial substrate (H2/CO2) pressure, from 100 to 500 kPa, on the SHMA, on CH4 production rate and on developed microbial communities were evaluated. Two different pressurized bioreactors were studied using anaerobic granular sludge as the biocatalyst and H2/CO2 (80:20, v/v) as sole carbon and energy source. Gaseous compounds were analyzed by GC and archaeal diversity within granular sludge was monitored by 16S r-RNA based techniques. Results: The results showed an increase in the SHMA as well as in the CH4 production rate with the increase of the initial H2/CO2 pressure. This results are very interesting since no inhibitory effects were observed on the microbial activity, demonstrating the resistance of the anaerobic granular sludge. The Illumina results showed that Methanosarcinales, Methanobacteriales and Methanomicrobiales were the three orders that prevailed in the pressurized system, for all the pressures tested. However, hydrogenotrophic methanogens from Methanobacterium and Methanospirillum genera slightly increased their relative abundance, varying from 38% (100 kPa) to 41% (500 kPa) and from 8% (100 kPa) to 12% (500 kPa), respectively. Conclusions: In conclusion, the archaeal community seems to be very stable when submitted to increasing H2/CO2 pressures, highlighting the potential of the anaerobic granular sludge as an efficient microbial platform for the production of added-value compounds from gaseous carbon waste streams.Portuguese Foundation for Science and Technology (FCT): POCI-01-0145-FEDER-031377; strategic funding of UIDB/04469/2020 unit; BioTecNorte operation (NORTE-01-0145-FEDER-000004); FCT doctoral grant PD/BD/128030/2016.info:eu-repo/semantics/publishedVersio

CH4 production at moderate H2/CO2 pressures - insights on the specific hydrogenotrophic methanogenic activity

CO2 is one of the main contributors to greenhouse gases (GHGs), being its emission to the atmosphere one of the major driver of global climate change. Biological methanation of CO2 using renewable H2 provides a promising approach to use of superplus renewable electrical power to produce a gaseous fuel. CH4 is considered an important renewable energy carrier, that has a wide range of applications such as natural gas for distribution. Hydrogenotrophic methanogens are key elements in the CO2/H2 methanation process. Thus the importance to study the specific hydrogenotrophic methanogenic activity (SHMA). The effect of the initial substrate (H2/CO2) pressure on the SHMA was investigated in two different pressurized bioreactors. The results suggest that in addition to the increase of the initial substrate pressure, also the bioreactor configuration influence the SHMA, which is crucial for the success of biological CO2 methanation technologies but also in anaerobic bioreactors treating wastewaters.info:eu-repo/semantics/publishedVersio

Inhibition of HMG-CoA reductase activity and cholesterol permeation through Caco-2 cells by caffeoylquinic acids from Vernonia condensata leaves

AbstractThe aim of this study was to provide scientific knowledge to support the use of Vernonia condensata Baker, Asteraceae, beverages for their alleged hypocholesterolemic properties by testing their action as HMG-CoA reductase inhibitors and their capacity to lower dietary cholesterol permeation. Chlorogenic acid, and other caffeoylquinic acids derivatives were identified as the main components of these beverages by LC–MS/MS. No changes in the composition were notice after the in vitro gastrointestinal digestion and no toxicity against Caco-2 and HepG2 cell lines was detected. Cholesterol permeation through Caco-2 monolayers was reduced in 37% in the presence of these herbal teas, and the caffeoylquinic acids permeated the monolayers in 30–40% of their initial amount in 6h. HMG-CoA reductase activity was reduced with these beverages, showing an IC50 of 217μgml−1. It was concluded that caffeoylquinic acids, the major components, justified 98% of the enzyme inhibition measured

Perspectives on syngas fermentation

Book of Abstracts of CEB Annual Meeting 2017The replacement of fossil fuels by renewable energy sources is, nowadays, a worldwide priority. Gasification processes and further bioconversion of syngas appears to be a promising alternative compared to the existing chemical techniques, since this process convert renewable sources into alternative fuels and commodity chemicals, such as CH4, fatty acids, alcohols, etc., additionally contributing to the reduction of greenhouse gases [1]. Nearly any form of organic matter can be transformed through gasification, into syngas, mainly composed of CO, H2 and CO2. The biological conversion of syngas offers several advantages over catalytic processes, specifically the greater resistance to catalyst poisoning and the higher specificity for the substrates [2]. Syngas- and CO-fermenting microorganisms use the Wood-Ljungdahl pathway to produce several multi-carbon compounds such as short- and medium-fatty acids and alcohols. Even though many studies were performed in the last few years, fermentation of syngas still involves practical challenges due to limitations of the process. The major bottleneck of syngas fermentation that blocks the commercialization of this technology is gas-to-liquid mass transfer limitations, since it reduces the microorganisms access to the substrate and consequently reduces the productivity rates. It is of utmost importance the development of alternatives that promote the enhancement of mass transfer, the improvement on the productivity rates from syngas fermentation and the deep study of the biocatalysts involved in syngas bioconversion pathways. Biological syngas conversion has been a research topic at the BRIDGE group since 2009, by studying both technological and microbiological aspects of the process. Previous work developed in our group focused on the use of anaerobic complex microbial communities to obtain enriched cultures and/or pure cultures that could convert syngas or CO into mainly acetate, CH4 and H2. Regarding to the technological aspects of syngas bioconversion process, a multi-orifice baffled bioreactor was used to study the effect of using different reactors designs to improve the gas-liquid mass transfer. Moreover, recent studies conducted at BRIDGE group with collaboration of BIOSYSTEMS group showed that the use of increased pressure (up to 5 bar) to increase gas-liquid mass transfer, leads to different metabolic routes on microorganisms. These results represent a step forward to direct the biochemical pathways of microbial community towards the specific products from syngas. As future perspectives, we aimed to continue a research line on syngas fermentation, by studying different operational approaches for this process and focusing on the production of butanol, 2,3-butanediol and propionate.info:eu-repo/semantics/publishedVersio

Exploring syntrophic relationships in the anaerobic biodegradation of lipids and long chain fatty acids

ICBM-3 - 3rd International Conference on Biogas Microbiology (Abstract Book)[Excerpt] Practical knowledge on anaerobic digestion of waste lipids has been improving for several decades, but the microbiology of these processes remains partially undisclosed, with non-cultivated taxonomic groups often detected in anaerobic communities degrading lipids. This work studies the diversity and physiology of anaerobic microorganisms involved in the metabolism of lipids and long chain fatty acids. Anaerobic culturing procedures were applied for the development of enrichment cultures, and combined with next generation sequencing techniques. Enriched microbial communities specialized in the degradation of triolein (0.3 mmol·L-1) and oleate (1 mmol·L-1) were obtained under methanogenic conditions. Oleatedegrading cultures were also developed in the presence of the external electron acceptors ferric hydroxide (75 mmol·L-1) or sulfate (15 mmol·L-1). Three mesophilic sludges from different origins were used as inocula. [...]info:eu-repo/semantics/publishedVersio

Co-cultivation of Thermoanaerobacter strains with a methanogenic partner enhances glycerol conversion

Glycerolrich waste streams produced by the biodiesel, bioethanol and oleochemical industries can be treated and valorized by anaerobic microbial communities to produce methane. As current knowledge of the microorganisms involved in thermophilic glycerol conversion to methane is scarce, thermophilic glyceroldegrading methanogenic communities were enriched. A coculture of Thermoanaerobacter and Methanothermobacter species was obtained, pointing to a nonobligately syntrophic glycerol degradation. This hypothesis was further studied by incubating Thermoanaerobacter brockii subsp. finnii and T. wiegelii with glycerol (10 mM) in pure culture and with different hydrogenotrophic methanogens. The presence of the methanogen accelerated glycerol fermentation by the two Thermoanaerobacter strains up to 3.3 mM day1, corresponding to 12 times higher volumetric glycerol depletion rates in the methanogenic cocultures than in the pure bacterial cultures. The catabolic pathways of glycerol conversion were identified by genome analysis of the two Thermoanaerobacter strains. NADH and reduced ferredoxin formed in the pathway are linked to proton reduction, which becomes thermodynamically favourable when the hydrogen partial pressure is kept low by the hydrogenotrophic methanogenic partner.The authors thank Ruben Gonçalves for preparing the thermophilic biomass and Andreia Salvador for the sup port with the microbial communities’ analysis. This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2019 unit, Project SAICTPAC/0040/2015 (POCI-01-0145-FEDER-016403) and BioTecNorte operation (NORTE-01-0145-FEDER 000004) funded by the European Regional Development Fund under the scope of Norte2020 – Programa Opera cional Regional do Norte. The authors also acknowledge the financial support of FCT and European Social Fund through the grants attributed to C.P. Magalhaes (SFRH/BD/132845/2017) and A.L. Arantes (PD/BD/128030/2016).info:eu-repo/semantics/publishedVersio

Microbial propionate production from carbon monoxide a novel bioprocess

Introduction: The fermentation of CO-rich gases by carboxidotrophic microbes is a promising way to produce valuable organic compounds. Propionate is a value-added compound with numerous industrial applications, e.g. as an antifungal agent in food and feed, and as a building block to produce plastics and herbicides. Propionate is currently produced by petrochemical processes, but it can be produced from ethanol and acetate by some propionogenic bacteria. Ethanol and acetate are usually formed by acetogenic bacteria from CO-rich gases. Accordingly, propionate can be indirectly produced from CO-rich gases, representing a new approach on the realm of microbial CO conversion. Methodology: Four distinct synthetic co-cultures were constructed, consisting of: Acetobacterium wieringae (DSM 1911T) and Pelobacter propionicus (DSM 2379T); A. wieringae (DSM 1911T) and Anaerotignum neopropionicum (DSM 3847T); A. wieringae strain JM and P. propionicus (DSM 2379T); A. wieringae strain JM and A. neopropionicum (DSM 3847T). The physiology of CO conversion to propionate was accessed and a proteogenomic analysis was performed in the best performing co-culture to get insight into the involved biochemical pathways and microbial interactions within the synthetic consortium. Results: Propionate was produced by all the co-cultures, with the highest titer (~24 mM) measured in the co-culture composed of A. wieringae strain JM + A. neopropionicum, which also produced isovalerate (~4 mM), butyrate (~1 mM), and isobutyrate (~0.3 mM). In this synthetic consortium, A. wieringae strain JM converts CO to a acetate and ethanol via the Wood-Ljungdahl pathway; acetate can also be converted to ethanol through the action of aldehyde oxidoreductase (AOR); A. neopropionicum converts ethanol to propionate via the acrylate pathway. In addition, proteins related to amino acid metabolism and stress response were highly abundant during co-cultivation, which raises the hypothesis that amino acids are exchanged by the two microorganisms, and this results in isovalerate and isobutyrate production. Conclusions: This synthetic co-culture represents a new bioprocess for the microbial production of propionate from carbon monoxide, that couples the Wood-Ljungdahl and acrylate pathways. Furthermore, this symbiosis engages an interesting perspective on how C1-fixing and C3-producing microorganisms can be used to expand the product scope of gas fermentation.Portuguese Foundation for Science and Technology (FCT): POCI-01-0145-FEDER-031377; strategic funding of UIDB/04469/2020 unit; BioTecNorte operation (NORTE-01-0145-FEDER-000004); FCT doctoral grants PD/BD/128030/2016 and PD/BD/150583/2020. Netherlands Science Foundation (NWO): Project NWO-GK-07; Perspectief Programma P16-10; Gravitation Grant, Project 024.002.002.info:eu-repo/semantics/publishedVersio

Effect of sub-stoichiometric Fe(III) amounts on LCFA degradation by methanogenic communities

Long-chain fatty acids (LCFA) are common contaminants in municipal and industrial wastewater that can be converted anaerobically to methane. A low hydrogen partial pressure is required for LCFA degradation by anaerobic bacteria, requiring the establishment of syntrophic relationships with hydrogenotrophic methanogens. However, high LCFA loads can inhibit methanogens, hindering biodegradation. Because it has been suggested that anaerobic degradation of these compounds may be enhanced by the presence of alternative electron acceptors, such as iron, we investigated the effect of sub-stoichiometric amounts of Fe(III) on oleate (C18:1 LCFA) degradation by suspended and granular methanogenic sludge. Fe(III) accelerated oleate biodegradation and hydrogenotrophic methanogenesis in the assays with suspended sludge, with H2-consuming methanogens coexisting with iron-reducing bacteria. On the other hand, acetoclastic methanogenesis was delayed by Fe(III). These effects were less evident with granular sludge, possibly due to its higher initial methanogenic activity relative to suspended sludge. Enrichments with close-to-stoichiometric amounts of Fe(III) resulted in a microbial community mainly composed of Geobacter, Syntrophomonas, and Methanobacterium genera, with relative abundances of 83–89%, 3–6%, and 0.2–10%, respectively. In these enrichments, oleate was biodegraded to acetate and coupled to iron-reduction and methane production, revealing novel microbial interactions between syntrophic LCFA-degrading bacteria, iron-reducing bacteria, and methanogens.Portuguese Foundation for Science and Technology (FCT) under the scope of project MORE (POCI-01-0145-FEDER-016575), of the strategic funding of UIDB/04469/2020 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020—Programa Operacional Regional do Norte. The authors also acknowledge the financial support of FCT and European Social Fund through the grants attributed to S.A. Silva (SFRH/BD/122623/2016), A.L. Arantes (PD/BD/128030/2016), and J.C. Sequeira (SFRH/BD/147271/2019)info:eu-repo/semantics/publishedVersio

Production of propionate from carbon monoxide by a synthetic co-culture

info:eu-repo/semantics/publishedVersio

Enhanced glycerol conversion by Thermoanaerobacter strains

Glycerol-rich waste streams produced as a surplus by the biodiesel industry can be treated and valorized by anaerobic microbial communities to produce biogas. Glycerol is a highly reduced compound. Its complete degradation to methane and carbon dioxide requires a syntrophic cooperation of anaerobic bacteria and archaea, either directly or through propionate, lactate or ethanol as intermediates. The aim of this work was to study glycerol valorization to methane by thermophilic microbial communities. Glycerol-degrading methanogenic communities were enriched at 55 ºC. A co-culture of Thermoanaerobacter and Methanothermobacter was obtained pointing to facultatively syntrophic glycerol degradation. This hypothesis was further tested by incubating Thermoanaerobacter brockii subsp. finnii and T. wiegelli type strains with glycerol (10 mmol L-1) in pure culture and with different hydrogenotrophic methanogens. The presence of the methanogen accelerated glycerol fermentation by the two Thermoanaerobacter strains up to 3.3 mmol L-1 day-1, corresponding to 12 times higher volumetric glycerol depletion rates in the methanogenic co-cultures than in pure bacterial cultures. The methanogen acted as a biological electron acceptor, which enhanced glycerol conversion by Thermoanaerobacter species, since it facilitates the redox balance and contributes to a higher energy gain of these bacteria. Therefore, syntrophic glycerol fermentation promotes faster anaerobic treatment of glycerol rich waste streams coupled to methane production.info:eu-repo/semantics/publishedVersio