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Comensoli, Lucrezia
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Comensoli, Lucrezia
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- PublicationAccès libreInteraction between microbes, iron and chlorine for the development of biotechnological approaches to stabilize corroded ironLes objets en fer subissent une inexorable oxydation, qui sans intervention de conservation-restauration cause une complète perte de l’objet en question. Ce phénomène concerne les superficies en fer, plusieurs infrastructures ainsi que les objets archéologiques. Nombreux méthodes sont disponibles pour la stabilisation de ces types de surfaces métalliques, toutefois, aucun n’est complétement efficace, et plusieurs ils emploient des substances toxiques. De plus, pour les surfaces exposées et les plomberies il n’existe pas un traitement définitif. Après seulement quelques années, ce genre d’infrastructures doit être retraité ou carrément remplacé. Cela cause des coûts de maintenance très élevés ainsi qu’un grand impact économique dans notre société. Concernant les objets archéologiques, il existe un problème supplémentaire. En effet, chaque objet constitue un témoignage unique du notre passé qui doit être protégé et étudié. Un objet archéologique est souvent unique et, si la restauration devait échouer, toutes les informations que l’objet pourrait révéler seraient perdues. Les scientifiques sont de l’avis qu’actuellement il n’existe pas un traitement efficace pour stabiliser le fer corrodé. Par conséquent, il y a une forte nécessité d’étudier et développer des nouvelles méthodes. Dans ce but, dans cette thèse, le potentiel des microorganismes (bactéries et champignons) pour le développement de nouvelles méthodes qui stabilisent le fer corrodé a été étudié. Étant donné qu’un des problèmes majeurs pour ce métal est le chlore, dans cette étude, l’efficacité de deux stratégies pour enlever cet élément depuis les objets et convertir les composées de corrosion instable en minéraux biogénique protecteurs, ont été évaluées.
La première approche, a été l’extraction indirecte du chlore en exploitant la capacité des microbes d’enlever les ions de fer présents dans les composées de corrosion contentant du chlore. Dans ce but, deux phénomènes ont été étudiés : la production microbiologique de minéraux biogénique et la capacité des champignons d’adsorber du fer dans leur biomasse. Plus précisément, en exploitant la production de minéraux biogéniques des souches TCE1 and LBE de la bactérie anaérobique Desulfitobacterium hafniense, il a été possible de convertir une partie de la couche de corrosion de plaques de fer et de clous archéologiques, en vivianite et magnétite. De plus, cette étude a aussi permis de conclure que les champignons ne sont pas les candidats les plus adéquats, pour le développement de méthodes de stabilisation du fer corrodé basés sur la production de cristaux biogéniques. En effet, en dépit du fait que Beauveria bassiana ait produit quelques cristaux, leurs quantité n’a pas été suffisante pour une précise caractérisation, et aucuns des facteurs testés a stimulé une production majeure. Toutefois, pour ce qui concerne l’adsorption de fer par les champignons, des résultats intéressants ont été obtenus. En effet, la capacité du champignon Alternaria sp. d’adsorber le fer a été utilisé avec succès pour le nettoyage de plaques corrodées. De plus, une application biotechnologique supplémentaire, qui exploite l’adsorption de fer par les champignons, a été étudiée. Dans cette étude, la capacité des bactéries d’utiliser le fer chélaté dans la biomasse fongique comme source de fer biodisponible a été prouvée avec la bactérie Pseudmonas fluorescens. Ce mécanisme, pourrait être utilisé pour améliorer la biodisponibilité de fer et la présence de carbone organique dans le sol pour les autres microorganismes, et peut-être aussi pour les plantes.
Ensuite, une deuxième approche concernant une méthode directe pour enlever le chlore a été étudiée. L’absorption de potassium et chlore a été prouvée pour B. bassiana, qui a produit des agrégats composés de ces deux éléments dans sa biomasse, quand exposé au FeCl2. Toutefois, cette capacité n’a pas pu être exploitée, car l’absorption de chlore n’était pas le mécanisme principal utilisé par ce champignon pour contraster la toxicité du chlore. En effet, il n’a pas été possible de mesurer une absorption suffisante de cet ion. Pour finir, la production de composés organiques volatiles a été explorée dans le but d’enlever le chlore du fer corrodé. Résultats préliminaires ont démontrés que le chlorure de sodium stimule la production de composés spécifiques, pas détectés en absence de cette substance. En général, on peut affirmer que cette étude a permis de montrer que les microorganismes sont une valable alternative pour la stabilisation du fer corrodé. Les bactéries peuvent être utilisées pour stabiliser la couche de corrosion en produisant des minéraux biogéniques stables, tandis que les champignons peuvent être employés pour le nettoyage du fer corrodé.
Abstract
Iron objects suffer inexorable oxidation and without any human intervention they would be completely damaged. This phenomenon occurs for iron surfaces, outdoor exposed structures as well as for archaeological iron objects. Several methods are currently available for the stabilisation of this type of metallic substrate, however, none of them is completely efficient, and several relay on the use of hazardous compounds. In addition, especially for outdoor iron and pipelines structure a permanent protective treatment does not exist. After few years these corroded surfaces have to be re-treated and in some cases replaced. This causes substantial maintenance costs having an important economic impact on our society. Regarding archaeological iron objects, an additional issue has to be considered. In fact, each object consists of a unique testimony of our past that should be preserved and studied. An archaeological object is usually unique and if the conservation interventions fail, all the information that the object could have revealed will be lost. Scientists agree with the fact that until now an efficient and durable stabilisation treatment for corroded iron does not exist. As a consequence, there is a pressing need to investigate new approaches. To this purpose, the present thesis investigated the potential of microorganisms (bacteria and fungi) for the development of stabilisation methods for corroded iron. Since one of the main issues for this metal is chlorine, this study examined two different strategies of chlorine removal and conversion of the unstable iron compounds into more stable biogenic minerals.
The first approach was an indirect chlorine extraction, consisting on the microbial removal of iron ions present in chlorinated corrosion compounds. For this purpose, microbial biogenic minerals production and fungal iron adsorption were investigated. In particular, exploiting biogenic minerals production of the strains TCE1 and LBE of the anaerobic bacterium Desulfitobacterium hafniense, it was possible to convert a part of the corrosion layer of corroded iron coupons, as well as of archaeological iron nails, into biogenic vivianite and magnetite. In addition, this study allowed definitely to assess that fungi are not the best candidates to develop stabilisation methods for corroded iron based on biogenic minerals production. In fact, even though Beauveria bassiana produced some biogenic crystals their amount was not sufficient for a precise characterisation, and none of the factors tested stimulated a higher production. Nevertheless, interesting results were obtained for fungal iron uptake. Indeed, iron uptake of the fungus Alternaria sp. was successfully used for a biocleaning of corroded iron coupons. In addition, another biotechnological application exploiting fungal iron uptake was investigated. In this study the ability of bacteria to use iron chelated in fungal dead biomass as a bioavailable source of iron was proved for Pseudomonas fluorescens. This could then be exploited to improve iron bioavailability, as well as availability of organic carbon in soil for other microbes and maybe also plants.
A second approach regarding a direct method for the removal of chlorine was also studied. Uptake of potassium and chlorine was proved for B. bassiana that produced aggregates containing these elements onto its biomass when exposed to FeCl2. However this ability could not be further exploited, as chlorine uptake was not the main resistance mechanism used by this fungus against chlorine, and an efficient uptake of this ion was not measured. Finally, aiming to remove chlorine from corroded iron, volatiles organic compounds production was studied. Preliminary results showed that NaCl stimulates the production of particular compounds not present in absence of this substance. Overall it can be affirmed that this study allow to assess that microorganisms are a valuable alternative for the stabilisation of corroded iron. Bacteria could be employed to stabilize the corrosion layer by producing stable biogenic minerals, while fungi could be used for biocleaning of corroded iron.
Riassunto
Gli oggetti in ferro sono soggetti ad un’inesorabile ossidazione e senza alcun intervento di restauro sarebbero completamente danneggiati. Questo fenomeno concerne superfici in ferro, strutture esposte all’esterno e anche oggetti archeologici. Svariati metodi sono disponibili per stabilizzare questo tipo di superfici metalliche, tuttavia, nessuna di questi è completamente efficiente, e numerosi necessitano l’uso di sostanze dannose per la salute. Inoltre, specialmente per le superfici esposte e le tubature in ferro, non esiste un trattamento protettivo definitivo. Dopo solamente qualche anno, questo tipo d’infrastrutture devono essere ritrattate o addirittura sostituite. Questo causa elevati costi di manutenzione e un grande impatto economico nella nostra società . Riguardo gli oggetti archeologici, esiste un problema aggiuntivo. Infatti, ogni oggetto rappresenta una testimonianza unica del nostro passato che dovrebbe venir protetta e studiata. Un oggetto archeologico è solitamente unico e, nel caso in cui il suo restauro dovesse fallire, tutte le informazioni racchiuse nel oggetto sarebbero perse. Gli scienziati concordano col fatto che attualmente non esiste un trattamento efficiente per stabilizzare il ferro corroso. Di conseguenza, esiste un crescente bisogno di studiare e sviluppare nouvi metodi. A questo scopo, nella presente tesi è stato studiato il potenziale dei microorganismi (batteri e funghi) per lo sviluppo di nuovi metodi che stabilizzino il ferro corroso. Siccome uno dei maggiori problemi per questo metallo è il cloro, nel presente studio sono state esaminate due strategie differenti per rimuovere questo elemento dagli oggetti e convertire i composti di corrosione instabili in minerali biogenici protettivi.
Il primo approccio è stato l’estrazione indiretta del cloro sfruttando la capacità dei microbi di rimuovere gli ioni di ferro presenti nei composti di corrosione contenenti cloro. A questo scopo, sono state studiate la produzione microbica di minerali biogenici e l’abilità dei fungi di adsorbire il ferro nella loro biomassa. In particolare, sfruttando la produzione di minerali biogenici dei ceppi TCE1 and LBE del battere anaerobico Desulfotobacterium hafniense, è stato possibile convertire una parte dello strato di corrosione sviluppatasi su placche di ferro e chiodi archeologici, in vivinite e magnetite. Questo studio ha inoltre permesso di concludere che i funghi non sono i migliori candidati per lo sviluppo di metodi di stabilizzazione del ferro corroso basati sulla produzione di cristalli biogenici. Infatti, nonostante Beauveria bassiana abbia prodotto qualche cristallo, la loro quantità non è stata sufficiente per una precisa identificazione, e nessuno dei fattori testati ne ha stimulato una maggiore produzione. Tuttavia, dei risultati interessanti, sono stati ottenuti con l’adsorbimento di ferro nei fungi. Infatti, l’abilità del fungo Alternaria sp. di adsorbire il ferro è stata usata con successo per la pulitura di placche corrose. Inoltre, è stata studiata un’ulteriore applicazione biotecnologica che sfrutta l’adsorbimento fungico di ferro. In questo studio, è stata verificata la capacità dei batteri di usare il ferro chelato nella biomassa morta dei fungi come fonte di ferro biodisponibile con il battere Peudomonas fluorescens. Questo meccanismo potrebbe venir sfruttato in futuro per migliorare la biodisponibilità del ferro e la presenza di carbonio organico nel suolo per altri microorganismi e magari anche per le piante.
Inseguito, un secondo approccio concernente un metodo diretto per la rimozione del cloro è stato studiato. L’assorbimento di potassio e cloro è stato dimostrato per B. Bassiana, che ha prodotto aggregati composti di questi elementi nella sua biomassa quando esposto al FeCl2. Tuttavia quest’abilità non ha potuto essere sfruttata inquanto l’assorbimento di cloro non è stato il principale meccanismo di resistenza usato da questo fungo per contrastare la tossicità del cloro. Infatti, non è stato possibile misurare un assorbimento considerevole di questo ione. In fine, la produzione di composti organici volatili è stata studiata allo scopo di rimuovere il cloro dal ferro corroso. Risultati preliminari hanno mostrato che il cloruro di sodio stimola la produzione di specifici composti, non presenti in assenza di questa sostanza. Complessivamente, si può affermare che questo studio ha permesso di dimostrare che i microorganismi costituiscono una valida alternativa per la stabilizzazione del ferro corroso. I batteri possono venir utilizzati per stabilizzare lo strato di corrosione producendo stabili minerali biogenici, mentre i funghi possono venir impiegati per la pulitura del ferro corroso. - PublicationMétadonnées seulementAssessment of a biological approach for the protection of copper alloys artefacts(Edinburgh: Historic Scotland and International Council of Museums, 2013)
; ; ; ; ; Wörle, MarieWe propose an innovative treatment by which the protection of copper-based artefacts can be provided by naturally occurring microorganisms. The properties of some fungi were exploited for the transformation of existing corrosion patinas into copper oxalates. The latter are known to be insoluble and chemically stable. Within the earlier EU-ARTECH and BAHAMAS projects, very promising results were obtained with an almost 100% conversion from copper hydroxysulfates and hydroxychlorides into copper oxalates. A fungal strain was used which had been isolated from vineyard soil heavily contaminated with copper. Further scientific investigations were carried out to determine the parameters of the process and allowing the formation of a reproducible and homogeneous patina of copper oxalates, called biopatina to highlight its biological origin. Particular attention was paid to the efficacy, durability and impact on colour of the newly developed treatment. Different copper and bronze coupons with either urban or marine patinas were prepared. Several analytical techniques were used for the characterisation of the patinas: Fourier Transform InfraRed microspectroscopy (µFTIR), colourimetry and Electrochemical Impedance Spectroscopy (EIS). The coupons were treated with either the biological treatment or reference materials (wax: Cosmoloid H80; silane: Dynasylan® F8263) and exposed to atmospheric corrosion (ISMAR-SMS Genoa Harbour, corrosivity class 5) in December 2011. The long-term behaviour and performance of the treatments under study was monitored and compared over a one year period using the same complement of analytical techniques used for the characterisation of the original patinas. These first measurements suggested a different weathering behaviour of the biopatina. In fact, in comparison to the silane and wax treatments the biopatina showed a lower colour variation, and a corrosion stabilisation process seemed to be in progress. A deeper analysis of colour and corrosion rate variation from different application methods was also achieved. The complete assessment of the different treatments will be finished this year. - PublicationAccès libreBacterial iron reduction and biogenic mineral formation for the stabilisation of corroded iron objects
; ; Exploiting bacterial metabolism for the stabilisation of corroded iron artefacts is a promising alternative to conventional conservation-restoration methods. Bacterial iron reduction coupled to biogenic mineral formation has been shown to promote the conversion of reactive into stable corrosion products that are integrated into the natural corrosion layer of the object. However, in order to stabilise iron corrosion, the formation of specific biogenic minerals is essential. In this study, we used the facultative anaerobe Shewanella loihica for the production of stable biogenic iron minerals under controlled chemical conditions. The biogenic formation of crystalline iron phosphates was observed after iron reduction in a solution containing Fe(III) citrate. When the same biological treatment was applied on corroded iron plates, a layer composed of iron phosphates and iron carbonates was formed. Surface and cross-section analyses demonstrated that these two stable corrosion products replaced 81% of the reactive corrosion layer after two weeks of treatment. Such results demonstrate the potential of a biological treatment in the development of a stabilisation method to preserve corroded iron objects.