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Exploring microalgal consortia within a circular economy model
No full textLe microalghe presentano un approccio versatile e sostenibile per affrontare le principali sfide ambientali, integrandosi perfettamente in un quadro di economia circolare. Questi microrganismi fotosintetici eccellono nella cattura del biossido di carbonio, nel risanamento dei flussi di rifiuti e nella produzione di composti ad alto valore, affermandosi come contributori chiave a sistemi più sostenibili. A differenza delle monocolture, i consorzi di microalghe sfruttano la diversità fisiologica di più specie, migliorando la resilienza e la produttività in diverse condizioni ambientali. L'equilibrio tra concorrenza e cooperazione al l'interno dei consorzi, guidato da interazioni tra specie come l'allelopatia, permette loro di adattarsi a condizioni difficili. Ciò rende i consorzi particolarmente efficaci nella fitorisanamento, generando al tempo stesso biomassa di alta qualità. La tesi mirava ad approfondire la comprensione dei consorzi di microalghe, dimostrando la loro superiorità sulle monocolture in termini di recupero dei nutrienti, crescita ed efficienza complessiva. La ricerca fa parte di un'iniziativa più ampia all'interno di un modello di economia circolare, in cui le microalghe sono utilizzate per risanare il digestato (un sottoprodotto liquido della digestione anaerobica) e la biomassa risultante viene riutilizzata come biostimolanti. Otto specie di alghe sono state inizialmente selezionate sulla base della loro capacità nota di risanare le acque reflue e del loro potenziale come biostimolanti. A seguito di un processo di selezione, è stato creato un consorzio delle specie più adatte, che superano le monocolture in termini di crescita. Le tre specie che compongono il consorzio (Tetradesmus obliquus, Chlamydomonas reinhardtii e Auxenochlorella protothecoides) hanno mostrato una minore tolleranza all'ammoniaca, una forma tossica di azoto nel digestato, se coltivate singolarmente rispetto al consorzio nel suo insieme. La riconfigurazione dell'abbondanza di specie all'interno del consorzio e l'attivazione di nuove vie metaboliche si sono dimostrate fondamentali per spiegare la sua resilienza superiore. Le indagini sulla comunicazione algale e l'allelopatia hanno rivelato il rilascio di vescicole extracellulari e il ruolo degli infochimici nel l'aumento dei tassi di crescita, della densità cellulare e della composizione della biomassa. Questi risultati hanno messo in evidenza i cambiamenti nei pool macromolecolari primari, sottolineando i meccanismi di adattamento del consorzio. La seconda parte della tesi si è concentrata sulle applicazioni biotecnologiche del consorzio in un contesto di economia circolare. Nel fitorisanamento, la coltivazione è stata ottimizzata esplorando parametri quali i sistemi di diluizione e immobilizzazione del digestato. La bonifica del digestato ha posto delle sfide a causa del suo elevato carico di nutrienti, della torbidità e della limitata penetrazione della luce. Una concentrazione di digestato del 7% è stata determinata per essere il massimo compatibile con la crescita significativa delle alghe. L'ottimizzazione successiva ha raggiunto alti tassi di rimozione per azoto e fosforo, anche se gli sforzi di immobilizzazione non sono riusciti a migliorare la produttività come previsto. Al di là della bonifica dei digestati, la tesi ha esplorato il potenziale agronomico dei biostimolanti microalgali. Le prove sperimentali, comprese la foliar spraying e il seed priming, hanno dimostrato che gli estratti di alghe migliorano la resa delle colture, migliorano la germinazione e ottimizzano l'assimilazione dei nutrienti. Gli studi fisiologici hanno rivelato differenze nelle risposte delle piante ai biostimolanti derivati da monocolture rispetto ai consorzi. Questi risultati hanno evidenziato la versatilità dei consorzi di microalghe e il loro potenziale per promuovere pratiche agricole sostenibili. Grazie alla loro adattabilità e multifunzionalità, i consorzi di microalghe incarnano i principi di un'economia circolare. Chiudono i circuiti dei nutrienti, riducono l'inquinamento ambientale e generano preziosi bioprodotti, fornendo un modello sostenibile che bilancia le priorità ecologiche ed economiche. Combinando la ricerca fondamentale con le applicazioni biotecnologiche, questo studio migliora in modo significativo la comprensione dei consorzi di microalghe, gettando le basi per future ricerche e applicazioni più ampie in questo campo.Microalgae present a versatile and sustainable approach to addressing major environmental challenges, seamlessly integrating into a circular economy framework. These photosynthetic microorganisms excel at capturing carbon dioxide, remediating waste streams, and producing high-value compounds, establishing themselves as key contributors to more sustainable systems. Unlike monocultures, microalgal consortia leverage the physiological diversity of multiple species, enhancing resilience and productivity across diverse environmental conditions. The balance between competition and cooperation within consortia, driven by interspecies interactions such as allelopathy, allows them to adapt to challenging conditions. This makes consortia particularly effective in phycoremediation while simultaneously generating high-quality biomass. The thesis aimed to deepen the understanding of microalgal consortia, demonstrating their superiority over monocultures in nutrient remediation, growth, and overall efficiency. The research forms part of a broader initiative within a circular economy model, where microalgae are used to remediate digestate (a liquid by-product of anaerobic digestion) and the resulting biomass is repurposed as biostimulants. Eight algal species were initially selected based on their known ability to remediate wastewater and their potential as biostimulants. Following a screening process, a consortium of the most suitable species was developed, outperforming monocultures in terms of growth. The three species constituting the consortium (Tetradesmus obliquus, Chlamydomonas reinhardtii, and Auxenochlorella protothecoides) showed lower tolerance to ammonia, a toxic nitrogen form in digestate, when grown individually compared to the consortium as a whole. The reconfiguration of species abundance within the consortium and activation of new metabolic pathways proved critical in explaining its superior resilience. Investigations into algal communication and allelopathy revealed the release of extracellular vesicles and the role of infochemicals in boosting growth rates, cell density, and biomass composition. These findings highlighted changes in the primary macromolecular pools, emphasizing the consortium's adaptive mechanisms. The second part of the thesis focused on biotechnological applications of the consortium in a circular economy context. In phycoremediation, cultivation was optimized by exploring parameters such as digestate dilution and immobilization systems. Digestate remediation posed challenges due to its high nutrient load, turbidity, and limited light penetration. A 7% digestate concentration was determined to be the maximum compatible with significant algal growth. Subsequent optimization achieved high removal rates for nitrogen and phosphorus, though immobilization efforts failed to enhance productivity as anticipated. Beyond digestate remediation, the thesis explored the agronomic potential of microalgal biostimulants. Experimental trials, including foliar spraying and seed priming, demonstrated that algal extracts improved crop yields, enhanced germination, and optimized nutrient assimilation. Physiological studies revealed differences in plant responses to biostimulants derived from monocultures versus consortia. These results underscored the versatility of microalgal consortia and their potential to advance sustainable agricultural practices. Through their adaptability and multifunctionality, microalgal consortia embody the principles of a circular economy. They close nutrient loops, mitigate environmental pollution, and generate valuable bioproducts, providing a sustainable model that balances ecological and economic priorities. By combining fundamental research with biotechnological applications, this study significantly enhances the understanding of microalgal consortia, laying the groundwork for future research and broader applications in this field.
Monocultures vs. polyculture of microalgae: unveiling physiological changes to facilitate growth in ammonium rich-medium
Full text linkDue to the increasing production of wastewater from human activities, the use of algal consortia for phytoremediation has become well-established over the past decade. Understanding how interspecific interactions and cultivation modes (monocultures vs. polyculture) influence algal growth and behaviour is a cutting-edge topic in both fundamental and applied science. Ammonium-rich growth media were used to challenge the monocultures of Auxenochlorella protothecoides, Chlamydomonas reinhardtii and Tetradesmus obliquus, as well as their polyculture; NO3− was also used as the sole nitrogen chemical form in control cultures. The study primarily compared the growth, carbon and nitrogen metabolisms, and protein content of the green microalgae monocultures to those of their consortium. Overall, the cultivation mode significantly affected all the measured parameters. Notably, at 50 mM NH4+, the assimilation rates of carbon and nitrogen were at least twice as high as those in the monoculture counterparts, and the protein content was three times more abundant.Additionally, the consortium's response to NH4+ toxicity was investigated by observing a linear relationship between the indicator of tolerance to NH4+ nutrition and the N isotopic signature. The study highlighted a high degree of acclimation through metabolic flexibility and diversity, as well as species abundance plasticity in the consortium, resulting in a functional resilience that would otherwise have been unattainable by the respective monoculture
Selection of microalgae in artificial digestate: Strategies towards an effective phycoremediation
Full text linkDigestate is a complex by-product of anaerobic digestion and its composition depends on the digestor inputs. It can be exploited as a sustainable source of nutrients for microalgae cultivation but its unbalanced composition and toxic elements make the use challenging. Screening algae in a simplified synthetic digestate which mimics the main nutrient constraints of a real digestate is proposed as a reproducible and effective method to select suitable species for real digestate valorisation and remediation. Growth performance, nutrient removal and biomass composition of eight microalgae exposed to high amounts of NH4+, PO4− and organic-C were assessed. Using a score matrix, A. protothecoides, T. obliquus, C. reinhardtii, and E. gracilis were identified as the most promising species. Thus, three strategies were applied to improve outcomes: i) establishment of an algal consortium to improve biomass production, ii) K+ addition to the medium to promote K+ uptake over NH4+ and to reduce potential NH4+ toxicity, iii) P starvation as pretreatment for enhanced P removal by luxury uptake. The consortium was able to implement a short-term response displaying higher biomass production than single species (3.77 and 1.03–1.89 mg mL−1 respectively) in synthetic digestate while maintaining similar nutrient remediation, furthermore, its growth rate was 1.6 times higher than in the control condition. However, the strategies aiming to reduce NH4+ toxicity and higher P removal were not successful except for single cases. The proposed algal screening and the resulting designed consortium were respectively a reliable method and a powerful tool towards sustainable real digestate remediatio
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
Fermentation of Microalgal Biomass for Innovative Food Production
Full text linkFermentation is an ancient method used worldwide to process and preserve food while enhancing its nutraceutical profile. Alga-based fermented products have recently been developed and tested due to growing interest in healthy sustainable diets, which demands the development of innovative practices in food production, operating for both human health and Earth sustainability. Algae, particularly microalgae such as Arthrospira platensis, Chlorella vulgaris, and Dunaliella salina, are already cultivated as sources of food due to their valuable compounds, including proteins, pigments, lipids, carotenoids, polyunsaturated fatty acids, steroids, and vitamins. Due to their nutritional composition, functional diversity, and flexible metabolism, microalgae represent good fermentation substrates for lactic acid bacteria (LAB) and yeasts. This review presents an overview of the scientific studies on microalga fermentation underlining microalgae’s properties and health benefits coupled with the advantages of LAB and yeast fermentation. The potential applications of and future perspectives on such functional foods 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
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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