Effects of conductive and non-conductive materials on the activity of a hydrogenotrophic methanogen

Several conductive materials (CM), such as carbon nanotubes (CNT), activated carbon (AC), and magnetite, have been reported to mediate interspecies electron transfer in methanogenic environments. However, CNT also accelerated methane production (MP) of pure cultures of methanogens. We hypothesize that other CM and also non-CM may affect the methanogenic activity of pure cultures. For that purpose, we incubated the hydrogenotrophic methanogen, Methanobacteriun formicicum strain DSM 1535T, with AC, zeolite (Zeo), sand and glass beads (at 0.5 g/L), and followed MP. All materials reduced lag phases preceding the MP, and the time for complete conversion of H2/CO2 to methane. The best results were obtained with Zeo, since total hydrogen conversion occurred in less than 5 days (instead of 8 days as in the control incubated without materials). Approximately 5 days with sand, and 6 days with glass beads and AC, were necessary to achieve the complete conversion. The lag phases with AC were quite short (1 day) when compared with the control assay without materials (5 days). The initial MP (determined during the first 3 days of incubation) was improved 16 times with Zeo and 11 times with AC, when compared with the cultures incubated without materials. The results show that there is not a direct relationship between conductivity and the improvement of methanogenic activity. Other physicochemical properties of the materials might be related with the beneficial effects towards methanogens.info:eu-repo/semantics/publishedVersio

Zeolite stimulates the activity of microbial enrichments converting butyrate to methane

Conductive materials have been tested as a strategy to improve methane production (MP) in anaerobic digestion (AD) processes1,2. The effect of zeolite (0.5 g/L) towards microbial enrichments converting butyrate (10 mmol/L) to methane was investigated and compared with a microbial enrichment in the absence of the material. The enrichments were initiated with granular anaerobic sludge from a brewery WWTP as inoculum. Incubations were carried out under strict anaerobic conditions (at 37 °C) and periodically transferred to fresh medium. The results showed that, after an initial adaptation period (3 transfers), the presence of zeolite significantly accelerated the total conversion of butyrate to methane, since it took approximately 30d with zeolite and around 45d without zeolite. However, both enrichment cultures after extended adaptation (more than 8 transfers) behaved similarly, degrading butyrate in approximately 15d. Nevertheless, zeolite addition to active butyrate enrichment cultures without previous contact with zeolite, slightly accelerated MP, while the highly adapted zeolite-enrichment decreased activity when incubated without zeolite. Thus, the presence of zeolite showed to stimulate the microbial activity enhancing MP from butyrate degradation. This material possess natural ion-exchange properties, absorptive capacity and could function as a support for biomass which makes its application very attractive to AD processes.info:eu-repo/semantics/publishedVersio

Pure cultures of hydrogenotrophic methanogens are affected by modified activated carbons, zeolite, sand and glass beads

The metabolism of hydrogenotrophs has been showed to be improved in the presence of carbon nanotubes, which is relevant since they are crucial microorganisms in the conversion of waste to methane1. In this study, we investigated if other materials, with different physicochemical properties, also affect the hydrogenotrophic activity of Methanobacterium formicicum. M. formicicum was incubated separately with 0.5 g/L of sand, and commercial zeolite, glass beads and activated carbon (AC0) with and without modifications on the AC0 surface. Modifications were obtained by chemical oxidation with HNO3 (AC_HNO3), H2SO4 (AC_ H2SO4) or both (AC_HNO3_ H2SO4) and thermal treatments. All materials, with exception of AC_HNO3_ H2SO4, improved the methanogenic activity. Carbon-based materials significantly reduced the lag phases preceding methane production (MP) (from approximately 5 days in the control to circa 1 day). Zeolite, sand and glass beads also reduced the lag phases but less than carbon materials (i.e., from 5 days to 1.5, 2.7 and 3.5 days, respectively). Additionally, exponential MP rates were up to 1.5 times higher in the assays with non-carbon materials. All materials tested have different physical/chemical properties including conductivities, but all stimulated the methanogenic activity. Thus, further studies are necessary to identify the mechanisms behind the underlying observations.info:eu-repo/semantics/publishedVersio

Modulation of butyrate-degrading methanogenic communities by conductive materials

Butyrate is a volatile fatty acid commonly present in anaerobic bioreactors. Previous research showed that methane production (MP) rates from butyrate, by lake sediment microbiomes, doubled by addition of carbon nanotubes, which was accompanied by changes in the microbial community composition, with enrichment of typical fatty-acid degrading bacteria (Syntrophomonas spp.), well known to exchange electrons with methanogens via hydrogen or formate formation1. But the authors suggested that electrons exchange via conductive materials (CM) may take place instead. In our study, anaerobic butyrate-degrading enrichment cultures were developed with other CM, namely activated carbon (AC) and magnetite (Mag) at 0.5 g/L. MP started earlier in AC enrichment and complete degradation was achieved faster in Mag enrichment. Syntrophomonas spp. were enriched in all cultures (representing 60 to 80 % of the total bacterial community), but hydrogenotrophic methanogens were highly stimulated by AC (78 % of Methanomicrobiales), while the methanogenic community of Mag culture was more diverse in acetoclastic methanogens (43% of Methanosarcina and Methanosaeta). It is still unclear if the improvement on butyrate degradation is associated to the role of CM in interspecies electron transfer, but it is undoubtful that they differentially modulate the methanogenic communities towards faster MP.info:eu-repo/semantics/publishedVersio

Differential effects of carbon-based and iron-based conductive materials in anaerobic butyrate-degrading enrichments

Introduction Conductive materials (CM) accelerate methane production (MP), probably by promoting more efficient interactions between bacteria and methanogens. This work investigates the effects of activated carbon (AC) and magnetite (Mag) in microbial enrichments degrading butyrate. Three different butyrate-degrading enrichments were developed: 1) without CM, 2) with AC, or 3) with Mag. It was also investigated if the effect of CM persisted when CM-adapted enrichments were transferred to new medium without CM, and if CM affected the activity of stable enrichments without previous contact with CM. Methodology Enrichment series were initiated with granular anaerobic sludge as inoculum, butyrate (10 mmol/L) as substrate, and CM (0.5 g/L AC or 0.5 g/L Mag), or without CM, and incubated at 37 °C, under strict anaerobic conditions. The following parameters were monitored: methane by gas chromatography; butyrate and acetate by high performance liquid chromatography; oxidation-reduction potential; pH and conductivity. RNA was extracted and taxonomic composition of the microbial communities was obtained by 16S rRNA gene sequencing. Results During the first incubations, AC-enrichment consumed hydrogen derived from butyrate degradation within 4 days, which was much faster than the enrichments with Mag and without CM, which presented lag phases (LP), preceding MP, longer than 11 and 7 days, respectively. Thus, Mag probably inhibited butyrate-degrading bacteria and/or hydrogenotrophic methanogens. Conversely, after the lag phase, Mag-enrichment was the fastest converting acetate to methane (3 times faster than in AC-enrichment), suggesting a stimulatory effect of Mag towards acetoclastic methanogens. Nevertheless, once the enrichments were adapted to the growth conditions, more efficient butyrate conversion was observed by all enrichments, with lag phases lower than 4 days, even in the control-enrichment. No significant changes on butyrate degradation were observed when highly adapted CM-enrichments were transferred to fresh medium without CM. On the other hand, when active enrichments (without previous contact with CM), were incubated with AC, it became slightly faster (0.7 times shorter LP), and with Mag were greatly inhibited (12 times longer LP). Syntrophomonas spp. represented 60 to 80 % of the total bacterial communities in all enrichments. Hydrogenotrophs were more abundant in AC-enrichment (78 % of Methanomicrobiales) and Mag-enrichment was highly enriched in acetoclastic methanogens (43 % of microorganisms assigned to Methanosaeta and Methanosarcina). Conclusions The presence of CM affects the performance of butyrate-degrading communities, with AC accelerating particularly butyrate conversion to methane (via H2/CO2) and acetate, and Mag inhibiting that first step but stimulating acetate conversion to methane.info:eu-repo/semantics/publishedVersio

Conductive materials affect methanogenic activity of pure cultures of methanogens and syntrophic cocultures

info:eu-repo/semantics/publishedVersio

Activated carbon and magnetite affect the methanogenic activity of acetoclastic and hydrogenotrophic methanogens

Conductive materials (CM) improve the efficiency of methane production (MP) in anaerobic digestion (AD) processes (Martins et al. 2018), but little is known on the impact of CM directly on methanogens. Different species of methanogens were shown to be differentially affected by carbon nanotubes (CNT) (Salvador et al. 2017; Zhang, Zhang, and Lu 2018). For instance, CNT increased significantly the activity of an hydrogenotrophic methanogen (Methanobacterium formicicum) (Salvador et al. 2017), but other methanogenic species were less affected (Salvador et al. 2017; Zhang, Zhang, and Lu 2018). In this study, we evaluated the effect of other CM (activated carbon (AC) and magnetite (Mag), at 0.5 g/L) on the activity of both hydrogenotrophic (M. formicicum and Methanospirillum hungatei) and acetoclastic (Methanosarcina barkeri and Methanosaeta harundinacea) pure cultures of methanogens. The presence of AC resulted in reduced lag phases preceding the MP, and faster initial MP rates (IMPR), which was more evident in M. formicicum cultures (IMPR increased 15 times). Magnetite inhibited the activity of M. formicicum, and showed a minor impact in the activity of the other methanogens.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit. Cátia S. N. Braga holds a grant SFRH/BD/132003/2017 funded by FCT and European Union (EU), through the Portuguese State Budget and the European Social Fund under the scope of Programa Operacional Regional do Norte. This work was also financially supported by: Base FundingUIDB/50020/2020 of the Associate Laboratory LSRELCM-funded by national funds through FCT/MCTES (PIDDAC). OSGPS acknowledges FCT funding under the Scientific Employment Stimulus-Institutional Call CEECINST/00049/2018.info:eu-repo/semantics/publishedVersio

Improving biomethane production by adding conductive nanomaterials

The search for renewable energy sources is one of the top priorities of humanity. Biomethane production through anaerobic digestion (AD) could help to reduce the dependence on fossil energy. The addition of conductive nanomaterials (CM) to AD systems results in the acceleration of methane production (MP) and in the improvement of the resilience of these systems. However, the mechanisms underlying this phenomenon are still unclear, particularly regarding the effects of materials on the activity of methanogens. The present work aimed to evaluate the effect of adding different carbon nanomaterials to a hydrogenotrophic and an acetoclastic culture. For this purpose, experiments were conducted with pure cultures of Methanobacterium formicicum and Methanosaeta harundinacea, in the presence and absence of 0.5 g/L of activated carbon (AC), carbon nanotubes (CNT), carbon black, graphite, and graphene. The experiments were conducted under strictly anaerobic conditions, and MP was monitored over time. In the assay with M. formicicum, the lag phase was shorter in all conditions with the presence of CM, compared to the control without CM. The initial MP rates reached values 11.6x, 9.4x, 6.4x, 6.3x, 5.3x, 3.0x and 2.1x higher than the control, with AC_300-500µm, AC_100-300µm, carbon black, AC_<100µm, graphite, graphene and CNT, respectively. Regarding the assay with M. harundinacea, the lag phases were also reduced with all the CM tested, and the MP rates were higher than the control in the presence of graphite and glassy carbon. In the presence of the other CM, the MP rate was also higher than the control, but in less extent. In conclusion, the presence of CM had a positive influence on both MP rates and the duration of the lag phase, and time of incubation.Portuguese Foundation for Science and Technology (FCT) under the scope of the CM4Methane project (Ref: PTDC/BTA-BTA/2249/2021; https://doi.org/10.54499/PTDC/BTA-BTA/2249/2021)info:eu-repo/semantics/publishedVersio

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved