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From CO2 to CH4 via biological methanation
No full textThe leitmotif of this Ph.D. thesis is represented by carbon dioxide (CO2) recycling via biological production of methane (CH4).
This work particularly focuses on the physiology of three hydrogenotrophic methanogens, Methanothermobacter marburgensis (M. marburgensis), Methanothermococcus okinawensis (M. okinawensis) and Methanococcus maripaludis S2 (M. maripaludis), that can be used as catalysts for biological methane production (BMP) process. This CO2 recycling method is challenging due to an inefficient transfer rate of molecular hydrogen (H2) from the gas phase to the liquid phase. Thus, the biocatalyst performance is limited by H2 availability in the liquid medium. However, several factors, as strain type and media requirements, operating conditions, and reactor design, can contribute to the success of CO2 conversion to CH4. Understanding the physiology of methanogens is a powerful tool for developing a scalable BMP process. Therefore, a novel study on the role of trace metals in pure cultures of M. okinawensis and M. marburgensis respectively is herein proposed. Experimental method of this study included an in silico analysis, closed batch, and fed-batch cultivations. In silico analysis revealed genomic differences among the transport systems and enzymes related to the methanogenesis pathway of these two methanogens. The importance of Fe as metal cofactor in methanogenesis emerged from the in silico analysis and it has been confirmed by the closed batch and fed-batch experiments. M. okinawensis responded to rising concentrations of trace element (TE) by increasing specific growth rate (μ, h-1) and volumetric productivity of methane (MER, mmolL-1h-1) during closed batch cultivation. Furthermore, M. okinawensis shown growth and CH4 in fed-batch cultivation. On the base of fed-batch cultures results, M. marburgensis was prioritized and applied for CO2-based BMP process optimization. It has been proposed a new feeding strategy based on exponential fed-batch cultivation where different medium-, TE- and sulphide dilution rates combinations, and different CO2/H2 inflow rates corresponded to a defined run. The specific setting of each run produced different responses from M. marburgensis. In this context, a MER of 476 mmol L-1 h-1 and μ of 0.69 h-1 were eventually achieved at highest H2/CO2 gassing rate and ratio. However, if these factors mitigate the limitation due to the H2 mass transfer on one side, they also reduce CH4 purity in the offgas on the other side. The combined effect of increasing TE dilution and H2/CO2 gassing rates positively affected the biomass and biomass concentration. Among trace elements, there are heavy metals whose toxicity is higher than others. Heavy metals can seriously affect the functionality of microorganisms, and therefore compromise their performances as biocatalysts of a bio-based process. Not only metals, but also organic compounds, such as carboxylic acids, can damage cells survival. Thus, the second experimental part of this thesis deals with inhibition studies on pure culture of M. maripaludis in closed batch cultivation. Despite the potential applications of M. maripaludis, the knowledge surrounding this strain runs out of lab-scale studies concerning the physiology and toxicology of heavy metals and VFAs. Therefore, M. maripaludis growth and productivity were tested by using copper (Cu), zinc (Zn), acetate (Ac) and propionic acid (Pr) as potential inhibitors of microbial activity. The culture was totally inhibited at concentration of 30, 70 and 100 mgL-1 of Cu and 0.7 and 1 gL-1 of Zn. However, M. maripaludis shows tolerance to 3, 7 and 10 mgL-1 of Cu with different extent. The addition of 0.3 gL-1 of Zn to the medium, rather promoted the biomass build-up of M. maripaludis and cancelled the effect of Cu when used together in the medium. In this study, it has been supported that the inhibition by Cu is due to a reduced or suppressed activity of the CODH/ACS complex producing acetyl-CoA intermediate. Acetyl-CoA is the precursor of many metabolic subsystems (e.g. lipid, amino acids, nucleotides pathways) and its alteration would interfere with them. While CODH/ACS activity is supported by CO2 and methanogenesis intermediate, the other way to produce acetyl-CoA is based on the acetate:CoA ligase. The relevance and the tolerance to rising concentrations of Ac and Pr was also investigated and quantified via HPLC analysis. Concentration of 5 and 10 mgL-1 of acetate did not inhibit nor growth neither productivity. Interestingly, the deprivation of acetate not only impacted on the growth rate but also on methanogenesis in M. maripaludis. In absence of Ac, the same concentrations of Pr caused a slow-down of the growth, while productivity was not touched. This study sheds light on the individual and combined impact of Cu, Zn, acetate and propionic acid on the metabolism of M. maripaludis. Furthermore, an attempt to define a possible mechanism which regulates specific acetate capture is provided in this study and the relevance of acetate:CoA ligase respect to CODH/ACS complex for acetyl-CoA synthesis is herein discussed. The information collected in this study are essential to improve the process efficiency of CO2 conversion to CH4 and extend the knowledge on the physiology of certain compounds. The tendency of these methanogens to adapt to adverse conditions, most of the time, offers the possibility to improve the engineering aspects of a limited process toward an unlimited one. Moreover, as a future activity, this thesis proposed the use of a 10-bar pressure bioreactor which has been projected in the frame of the Ph.D. research with a view to improving the success of biological CH4 production
A Microbial-Centric View of Mobile Phones: Enhancing the Technological Feasibility of Biotechnological Recovery of Critical Metals
Full text linkEnd-of-life (EoL) mobile phones represent a valuable reservoir of critical raw materials at higher concentrations compared to primary ores. This review emphasizes the critical need to transition from single-material recovery approaches to comprehensive, holistic strategies for recycling EoL mobile phones. In response to the call for sustainable techniques with reduced energy consumption and pollutant emissions, biohydrometallurgy emerges as a promising solution. The present work intends to review the most relevant studies focusing on the exploitation of microbial consortia in bioleaching and biorecovery processes. All living organisms need macro- and micronutrients for their metabolic functionalities, including some of the elements contained in mobile phones. By exploring the interactions between microbial communities and the diverse elements found in mobile phones, this paper establishes a microbial-centric perspective by connecting each element of each layer to their role in the microbial cell system. A special focus is dedicated to the concepts of ecodesign and modularity as key requirements in electronics to potentially increase selectivity of microbial consortia in the bioleaching process. By bridging microbial science with sustainable design, this review proposes an innovative roadmap to optimize metal recovery, aligning with the principles of the circular economy and advancing scalable biotechnological solutions for electronic waste management
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Perspective on the use of methanogens in lithium recovery from brines
Full text link: Methanogenic archaea stand out as multipurpose biocatalysts for different applications in wide-ranging industrial sectors due to their crucial role in the methane (CH4) cycle and ubiquity in natural environments. The increasing demand for raw materials required by the manufacturing sector (i.e., metals-, concrete-, chemicals-, plastic- and lubricants-based industries) represents a milestone for the global economy and one of the main sources of CO2 emissions. Recovery of critical raw materials (CRMs) from byproducts generated along their supply chain, rather than massive mining operations for mineral extraction and metal smelting, represents a sustainable choice. Demand for lithium (Li), included among CRMs in 2023, grew by 17.1% in the last decades, mostly due to its application in rechargeable lithium-ion batteries. In addition to mineral deposits, the natural resources of Li comprise water, ranging from low Li concentrations (seawater and freshwater) to higher ones (salt lakes and artificial brines). Brines from water desalination can be high in Li content which can be recovered. However, biological brine treatment is not a popular methodology. The methanogenic community has already demonstrated its ability to recover several CRMs which are not essential to their metabolism. Here, we attempt to interconnect the well-established biomethanation process with Li recovery from brines, by analyzing the methanogenic species which may be suitable to grow in brine-like environments and the corresponding mechanism of recovery. Moreover, key factors which should be considered to establish the techno-economic feasibility of this process are here discussed
Novel insights in dimethyl carbonate-based extraction of polyhydroxybutyrate (PHB)
Full text linkBackground: Plastic plays a crucial role in everyday life of human living, nevertheless it represents an undeniable
source of land and water pollution. Polyhydroxybutyrate (PHB) is a bio-based and biodegradable polyester, which can
be naturally produced by microorganisms capable of converting and accumulating carbon as intracellular granules.
Hence, PHB-producing strains stand out as an alternative source to fossil-derived counterparts. However, the extraction
strategy affects the recovery efficiency and the quality of PHB. In this study, PHB was produced by a genetically
modified Escherichia coli strain and successively extracted using dimethyl carbonate (DMC) and ethanol as alternative
solvent and polishing agent to chloroform and hexane. Eventually, a Life Cycle Assessment (LCA) study was performed
for evaluating the environmental and health impact of using DMC.
Results: Extraction yield and purity of PHB obtained via DMC, were quantified, and compared with those obtained
via chloroform-based extraction. PHB yield values from DMC-based extraction were similar to or higher than those
achieved by using chloroform (≥ 67%). To optimize the performance of extraction via DMC, different experimental
conditions were tested, varying the biomass state (dry or wet) and the mixing time, in presence or in absence of a
paper filter. Among 60, 90, 120 min, the mid-value allowed to achieve high extraction yield, both for dry and wet
biomass. Physical and molecular dependence on the biomass state and solvent/antisolvent choice was established.
The comparative LCA analysis promoted the application of DMC/ethanol rather than chloroform/hexane, as the best
choice in terms of health prevention. However, an elevated impact score was achieved by DMC in the environmentallike
categories in contrast with a minor contribution by its counterpart.
Conclusion: The multifaceted exploration of DMC-based PHB extraction herein reported extends the knowledge of
the variables affecting PHB purification process. This work offers novel and valuable insights into PHB extraction process,
including environmental aspects not discussed so far. The findings of our research question the DMC as a green
solvent, though also the choice of the antisolvent can influence the impact on the examined categories.This work has been funded by the Horizon 2020 EU Framework Programme:
CELBICON project, Grant agreement number: 679050. Open access funding
provided by PRIME project funded by the POR FESR 2014/2020 Programme,
Asse I – Azione I.1b.2.2 Regione Piemonte, within the Piattaforma Tecnologica
per la Bioeconomia.Publicad
Assessing the methanogenic activity of microbial communities enriched from a depleted reservoir
Full text linkUsing a depleted gas reservoir as a natural reactor is a novel approach for microbial methanation of hydrogen (H2) and carbon dioxide (CO2) into methane (CH4). This approach, known as underground biomethanation reactor (UMR), could enable the simultaneous valorization of geologically sequestered CO2 and the excess renewable energy, stored in the form of H2 in the same formation as the CO2. In this study, we explore the possibility to trigger biomethanation from formation water sample by testing various carbon sources (CO2, trypticase peptone, glucose, and acetate) in batch test with a defined mineral medium. Obtained results show that trypticase peptone supplementation greatly increased methane production and the enrichment of methanogenic archaea, outperforming alternative carbon sources. 16S rRNA amplicon sequencing of the enriched consortia revealed that supplementation of trypticase peptone and a mixture of H2:CO2 (80:20), resulted in the selection of a mixed culture dominated by microorganisms assigned to the Methanothermobacterium, Garciella, and Caminicella genera. Furthermore, KEGG (Kyoto Encyclopedia of Genes and Genomes) and COG (Clusters of Orthologous Genes) predictive functional analyses underline a possible syntrophic relationship, enhancing the conversion of H2 and CO2 into CH4. This work lays the groundwork for biologically exploiting a depleted gas reservoir by implementing the UMR technology
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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