Thesis (PhD) -- Macquarie University, Division of Environmental and Life Sciences, Dept. of Chemistry and Biomolecular Sciences, 2007. / Bibliography: leaves 295-322. / Generation of peroxide groups in proteins exposed to a wide variety of reactive oxygen species (ROS) requires an initial formation of protein carbon-centred or peroxyl free radicals, which can be reduced to hydroperoxides. Both protein radicals and protein hydroperoxides are capable of oxidizing important biomolecules and thus initiate biological damage. In this study, we investigated the inhibition of protein hydroperoxide formation by ascorbate and GSH in gamma-irradiated HL-60 cells.--We used HL-60 cells as a model for general protection of living organisms by ascorbate (Asc) and glutathione (GSH) from the deleterious effects of protein hydroperoxides generated by radicals produced by gamma radiation. Measurement by HPLC indicated that incubation of HL-60 cells with Asc in the presence of ascorbate oxidase resulted in the accumulation of intracellular Asc. The intracellular Asc levels were lowered by irradiation, demonstrating intracellular consumption of Asc by the radiation-generated radicals. Exposure of HL-60 cells to increasing gamma irradiation doses resulted in increasing accumulation of protein peroxides in the cells. This was measured by the FOX assay. A significant decrease in intracellular protein hydroperoxides was noted when the cells were treated with ascorbic acid before irradiation. A dose-dependent protective effect of Asc was observed. Asc loading also provided strong protection from radiation-generated protein hydroperoxides independently of the composition of the external medium, showing that only the radicals formed within the cells were effective in oxidizing the cell proteins. Similarly, protein peroxidation was inhibited in cells with enhanced levels of GSH and increased when the intracellular GSH concentration was reduced. These findings indicate that ascorbate and GSH are important antioxidants in protecting cells from oxidative stress associated with the generation of protein hydroperoxide. / Mode of access: World Wide Web. / xxix, 322 leaves ill

Une part importante de la détérioration des réseaux d’assainissement en matériau cimentaire est d’origine biologique. Dans ce contexte, les matériaux à base de ciment alumineux ont montré une meilleure durabilité que ceux à base de ciment Portland ordinaire, couramment utilisés. Les hypothèses de la littérature qui expliqueraient cette meilleure résistance sont centré sur l’aluminium (présent à plus de 50% dans les ciments alumineux pour seulement 5% dans les ciments Portland). L’objectif de cette thèse est de caractériser et hiérarchiser les mécanismes de résistance des matériaux cimentaires lors de la biodétérioration. Cela permettra de comprendre le rôle de l’aluminium dans les interactions entre les microorganismes et les matériaux cimentaires. Après des études en réacteur et des tests de biodétérioration de pâte de ciments en laboratoire, il semblerait que la principale cause de résistance est due à la réactivité des matrices cimentaires plus qu’à un effet inhibiteur de l’aluminium ou du matériau sur les microorganismes. / An important part of the deterioration observed in concrete sewer networks is due to biological activity. In this context, calcium aluminate cement (CAC) based material has shown a better durability than ordinary Portland cement, usually used in such context. In literature, hypothesis explaining the better resistance are focused on aluminium. The aim of the project is to characterize the role of aluminium in the interactions between cementitious material and microorganisms. Reactor study and Lab scale aggressive biodeterioration protocol of cementitious material revealed that the better resistance of CAC is due to their lower reactivity and not to a bacteriostatic effect of the material on the microorganisms.

O presente estudo teve como objetivo avaliar a comunidade envolvida na desnitrificação autotrófica pela oxidação de sulfetos, aplicada ao pós-tratamento de efluentes anaeróbios. O enriquecimento da comunidade bacteriana e da comunidade desnitrificante autotrófica foi realizado a partir de amostras da biomassa coletadas de três reatores verticais de leito fixo operados em condições distintas, sendo, redução autotrófica de nitrato, redução autotrófica de nitrito e redução autotrófica de nitrato com excesso de sulfeto. Após a determinação da melhor condição de enriquecimento, a cultura foi purificada, identificada por meio de ferramentas da biologia molecular e caracterizada quanto às melhores condições de crescimento. O enriquecimento foi bem sucedido com a biomassa dos três reatores. No entanto, a condição de redução de nitrato com relação \'N\'/\'S\' igual a 0,8 foi a que apresentou maior concentração de microrganismos desnitrificantes autotróficos. A bactéria isolada foi identificada como Pseudomonas stutzeri. A velocidade específica máxima de crescimento da cultura (\'mü\'máx) foi de 0,037/h, com tempo de duplicação de 18,7 horas. O rendimento celular (Y) do composto nitrogenado foi de 0,15 gSSV.g/\'N\' e a velocidade de desnitrificação foi de aproximadamente 0,24 g\'N\'/gSSV.h. Os dados obtidos indicaram a viabilidade da aplicação da espécie isolada no processo de desnitrificação autotrófica utilizando sulfeto como doador de elétrons. / The aim of this study was to evaluate the community involved on autotrophic denitrification by sulfide oxidation applied to the post-treatment of anaerobic effluents. The enrichment of the bacterial community and autotrophic denitrifier community was accessed in three immobilized bed reactors operated at the conditions of autotrophic reduction of nitrate, autotrophic reduction of nitrite and autotrophic reduction of nitrate under excess of sulfide. Following the determination of the best enrichment conditions, the culture was purified, identified by molecular biology tools and the best growth conditions were characterized. Enriched cultures were obtained for the three operational conditions, but the best condition for the growth of autotrophic denitrifiers microorganisms was at \'N\'/\'S\' ratio of 0,8. The isolated microorganism was identified as Pseudomonas stutzeri. The maximum specific growth rate (\'mü\'máx) was 0.037/h, with a doubling time of 18.7 hours. The growth yield (Y) of nitrogen compound was 0.15 gSSV/g\'N\' and the specific rate of nitrogen utilization was approximately 0.24 g\'N\'/gSSV.h. The results indicated the viability of application of this microorganism for autotrophic denitrification using sulfide as electron donor.

No description available.

Pelagic aggregates function as biological carbon pumps for transporting fixed organic carbon to sediments. In iron-rich (ferruginous) lakes, photoferrotrophic and chemolithoautotrophic bacteria contribute to CO2 fixation by oxidizing reduced iron, leading to the formation of iron-rich pelagic aggregates (iron snow). The significance of iron oxidizers in carbon fixation, their general role in iron snow functioning and the flow of carbon within iron snow is still unclear. Here, we combined a two-year metatranscriptome analysis of iron snow collected from an acidic lake with protein-based stable isotope probing to determine general metabolic activities and to trace 13CO2 incorporation in iron snow over time under oxic and anoxic conditions. mRNA-derived metatranscriptome of iron snow identified four key players (Leptospirillum, Ferrovum, Acidithrix, Acidiphilium) with relative abundances (59.6–85.7%) encoding ecologically relevant pathways, including carbon fixation and polysaccharide biosynthesis. No transcriptional activity for carbon fixation from archaea or eukaryotes was detected. 13CO2 incorporation studies identified active chemolithoautotroph Ferrovum under both conditions. Only 1.0–5.3% relative 13C abundances were found in heterotrophic Acidiphilium and Acidocella under oxic conditions. These data show that iron oxidizers play an important role in CO2 fixation, but the majority of fixed C will be directly transported to the sediment without feeding heterotrophs in the water column in acidic ferruginous lakes.

<p>This doctoral research comparatively assesses the biogeochemical properties of suspended aquatic flocs through a integrated field-laboratory approach; providing new insight into the linkages among floc associated bacteria, floc-reactive solid phases and trace metal uptake.</p> <p>Results show flocs to possess a distinct geochemistry, microbiology and composition from bed sedimentary materials in close proximity (III-oxyhydroxide minerals (FeOOH); resulting in localized floc-Fe-mineral precipitates and enhanced reactivity. Further, the Fe-enrichment of floc and of floc bio-mineral constituents in turn provides an important and novel lens through which to examine how environmental microbial communities, microbial metabolism and Fe^III/Fe^IIredox transformations interact. The results were the discovery of floc-hosted, Fe^III/II-redox cycling bacterial consortia across diverse oxygenated (O₂^Sat.=1-103%) aquatic systems, which were not predicted to sustain bacterial Fe-metabolism. Both environmental<em> </em>and experimentally-developed consortial aggregates constituted multiple genera of aero-intolerant Fe^III-reducing and Fe^II-oxidizing bacteria together with oxygen consuming organotrophic species. These findings highlight that the implementation of geochemical thermodynamic constraints alone as a guide to investigating and interpreting microbe-geosphere interactions may not accurately capture processes occurring <em>in situ.</em></p> <p><em> </em> Seasonal investigation of microbial Fe^III/II-redox transformations highlighted the interdependence of floc Fe-redox cycling consortia members, revealing that cold conditions and a turnover in putative Fe-reducing community membership extinguishes the potential for coupled Fe-redox cycling by wintertime floc bacteria. Further, the observed summer-winter seasonal turnover of <em>in situ</em> floc community membership corresponded with an overall shift from dominant Fe to S redox cycling bacterial communities. This significantly impacted observable floc Fe and TE (Cd, Pb) geochemistry, resulting in a shift in floc associated Fe-phases from dominantly Fe^(III)_(s) to Fe^(II)_(s), and, in turn, corresponded to a large decrease of TE uptake by flocs under ice.</p> / Doctor of Science (PhD)

Reconnu par leur effet toxique, inhibiteur et corrosif, les sulfures (S2-, SH-, SH2) sont un sous-produit indésirable de la digestion anaérobie des boues de station de traitement des eaux domestiques de la ville de Marrakech, Maroc (STEP). Ils proviennent essentiellement de la réduction "dissimilatrice" des composés soufrés (SO4 2-, SO3 2-, S2O4 2- ..) contenus dans ces boues. Ce processus est réalisé par un groupe bactérien anaérobie appelé bactéries sulfatoréductrices (BSR). Une fois dans le biogaz, les sulfures sous forme gazeuse réduisent en plus la durée de vie des installations et des équipements de la STEP. Elle est ainsi dotée d’installations biologiques et physico-chimiques lui permettant d’éliminer ces sulfures avant la transformation du biogaz en énergie électrique. Cependant, ces procédés sont onéreuses et grandes consommatrices d’énergies. D’où l’idée de minimiser la production des sulfures au sein même des digesteurs anaérobies. Pour cela, il était nécessaire d’abord de connaître les microorganismes à l'origine de la production des sulfures (BSR), ceux potentiellement impliqués dans leur élimination (bactéries sulfo-oxydantes), et d’un groupe de microorganismes fermentaires (Synergistetes) intervenant dans le bon fonctionnement de la digestion anaérobie. Ces études ont été menées à la fois sur des d'approches moléculaires et culturales. Les résultats obtenus, ont permis de comprendre comment ces groupes bactériens, d’intérêts écologique et économique importants, interviennent dans la digestion anaérobie des boues de la STEP permettant à la fois d’accélérer les processus d’oxydation de la matière organique combinée à la réduction des composés soufrés et de minimiser la concentration des en sulfure dans le biogaz. / Recognized by their toxic, inhibitory and corrosive effect, sulfides (S2-, SH-, H2S) are an undesirable by-product of the anaerobic digestion of from domestic wastewater treatment plants sludge in the city of Marrakech, Morocco (WWTP). They produced mainly by the dissimilatory reduction of sulfur compounds (SO42-, SO32-, S2O42-) contained in these sludges. This process is performed by an anaerobic bacterial group called sulfate reducing bacteria (SRB). Once in the biogas, the sulfides in gaseous form shorten in addition the lifetime of the installations and equipments of the WWTP. It is thus equipped with biological and physicochemical installations allowing it to eliminate these sulfides before the transformation of biogas into electrical energy. However, these processes are expensive and consume large amounts of energy. Hence the idea of minimizing the production of sulfides within anaerobic digesters. For this, it was first necessary to know the microorganisms originating of the production of sulfides (SRB), those potentially involved in their elimination (sulfur oxidizing bacteria), and a group of fermentative microorganisms (Synergistetes) involved in the good functioning of the anaerobic digestion. These studies were conducted on both molecular and cultural approaches. The results obtained allowed to understand how these bacterial groups, of great ecological and economic interest, are involved in the anaerobic digestion of sludge from the WWTP, which both accelerates the oxidation processes of the organic matter combined with the reduction of sulfur compounds and to minimize the concentration of sulfide in biogas.

<p>Proces pečenja u proizvodnji keramičkog crepa u većini slučajeva se izvodi u<br />oksidavionoj atmosferi. Dobijena mikrostruktura koja obezbeđuje najvažnije osobine<br />primene zavisi od mineralo&scaron;kog sastava polaznog materijala i temperature termičkog<br />tretmana.<br />Sa stanovi&scaron;ta proizvodnje glinenog crepa, sirovina sa značajnim sadržajem karbonata kao &scaron;to je kop gline u Kanjiži, predstavlja problem te se ne može koristiti u njenom prirodnom sastavu. U oksidacionom termičkom tretmanu, staklasta faza koja se formira razgradnjom lakotopivih glinenih minerala ne kvasi u dovoljnoj meri zemnoalkalne okside nastale razgradnjom karbonata. Očekivane nove kristalne faze, kao &scaron;to su gelenit i anortit, koje predstavljaju osnovu dobrih tehničkih osobina crepa, ne mogu nastati u potrebnoj količini. Jedno od re&scaron;enja ovog problema je pobolj&scaron;anje interakcije između silikata i CaO/MgO promenom kvaliteta atmosfere pečenja.<br />Cilj je bio da se dobije odgovor na pitanje, da li se mogu promenom tehnolo&scaron;kih<br />parametara pečenja pobolj&scaron;ati karakteristike finalnog proizvoda dobijenog od sirovinske sme&scaron;e sa visokim masenim udelom karbonata.<br />Dati su rezultati pečenja u oksidacionoj i redukcionoj atmosferi u pogledu fizičkomehaničkih karakteristika i nastanka novih kristalnih faza. U radu su primenjene metode 57Fe M&ouml;ssbauer spektroskopije, difrakcija X zraka i dilatometrijska analiza za<br />identifikaciju promena faza tokom pečenja u oksidacionoj i redukcionoj atmosferi<br />(CO/N2 atmosfera) na temperaturama od 700-1060&deg;C. Ove promene reflektuju<br />dehidroksilaciju glinenih minerala, dekompoziciju karbonata, denzifikaciju i formiranje<br />novih kristalnih faza (plagioklasi). U cilju analize industrijskih uzoraka, pored 57Fe<br />M&ouml;ssbauer spektroskopije, primenjene su i sledeće metode: skenirajuća elektronska<br />mikroskopija (SEM) sa EDS analizom, živina porozimetrija, fotoelektronska spektroskopija (XPS) i karakterizacija apsorbcije vode, otpornosti na mraz i nosivosti.<br />Primena redukujuće atmosfere pokazala se kao opravdana, dobijen je glineni crep<br />pobolj&scaron;anih karakteristika u odnosu na standardni proizvod pečen u oksidacionoj<br />atmosferi.</p> / <p>The firing process in clay roofing tile production is normally carried out in oxidizing<br />firing atmosphere. The obtained microstructure which provides the most important<br />properties of the application depends on the mineralogical composition of the starting raw material and the firing temperature.<br />Concerning the production of roofing tiles, clay raw materials with a high content of<br />carbonates such as the Kanjiza clay material, possess an inappropriate composition. The melt phase is formed after the decomposition of clay minerals during the common firing process. This liquid phase, due to its extent wetting characteristics, is not able to wet properly the earth alkali oxides obtained after the decomposition of the carbonates. The expected new crystalline phases, like gehlenite and anorthite, which are needed for the favorable technical properties of the roofing tiles, can not be formed in the required quality and quantity. One solution to this problem is the limebonding improvement by changing the conditions of the firing atmosphere.<br />The main aim of this work is to examine the effects of firing conditions on the<br />properties of clay roofing tiles with high carbonate content. The obtained physical and<br />mechanical properties and the obtained new crystalline phases are described in detail.<br />The experiment used dilatometry, X-ray diffractometry, 57Fe M&ouml;ssbauer<br />spectroscopy to identify the changes during the firing process in oxidizing and<br />reducing atmosphere (CO/N2 atmosphere) at temperatures between 700 and 1060&deg;C.<br />Furthermore, for industrial sample analysis, scanning electronmicroscopy with EDS,<br />XPS, Hg porosimetry, water absorption procedure, frost resistance and bending<br />measurements were applied.<br />The application of reducing atmosphere was proved to be valid. The obtained<br />roofing tiles had improved properties compared to the standard production which uses<br />oxidizing firing atmosphere.</p>

Les travaux de recherche effectués lors de cette thèse portent sur l’obtention de nanotubes de carbone ultracourts et leur biofonctionnalisation pour une utilisation comme biomarqueur proche infrarouge. Des dispersions de nanotubes de carbone en milieux aqueux ont été formulées à l’aide de différents tensioactifs. Un traitement chimique oxydant préalable et/ou l’application d’ultrasons aux nanotubes ont permis de réduire leur longueur de façon significative, la sélection des plus courts étant effectuée par ultracentrifugation en gradient de densité. Les différentes fractions sélectionnées à l’issu de ce processus ont été caractérisées par spectroscopie Raman et spectroscopie d’absorption ainsi que par microscopie à force atomique. Il est ainsi montré la sélection de nanotubes d’une longueur inférieure à 20 nm. Nous montrons également leur fonctionnalisation à l’aide d’anticorps monoclonaux et leur visualisation par imagerie photothermique hétérodyne. Des résultats prometteurs ont été obtenus avec la fixation spécifique de nanotubes de carbone ultracourts sur des cellules. Ces travaux ouvrent de nombreuses perspectives en bioimagerie et en particulier l’étude de la plasticité synaptique au sein de neurones vivants. / This thesis reports the achievement of ultrashort carbon nanotubes and their biofunctionalization for applications as near-infrared biomarker. Dispersions of carbon nanotubes in aqueous media have been formulated with various surfactants. Oxidizing chemical treatments combined with the application of ultrasounds allowed significant shortening of the carbon nanotubes. Sorting and selection of the shortest nanotubes was done by density gradient ultracentrifugation. The different fractions selected at the end of this process have been characterized by Raman spectroscopy, UV-vis absorption spectroscopy and atomic force microscopy. Selection of nanotubes of a length below 20 nm is demonstrated. We also show functionalization by antibodies and the visualization of ultrashort functionalized nanotubes by photothermal heterodyne imaging. Promising results were obtained with the specific binding of ultrashort carbon nanotubes to cells. This work open route towards bioimaging applications and in particular towards the study of the synapsis plasticity within alive neurons.

Ecosystems currently face widespread biodiversity losses and other environmental disturbances, such as climate warming, related to increased anthropogenic activities. Within this context, scientists consider the effects of such changes on the biodiversity, and hence on the activity, of soil microorganisms. Indeed, soil microorganisms mediate a wide range of soil processes. Currently, knowledge on soil microbial diversity is still limited, partially due to technical limitations. The advent of molecular-based analyses now allows studying the soil microbial diversity. These advances in the study of soil microbial communities have lead to a growing evidence of the critical role played by the microbial community in ecosystem functioning. This relationship is supposed to be relevant for narrow processes, regulated by a restricted group of microorganisms, such as the nitrification process. This PhD thesis aimed at studying ammonia oxidizing bacteria (AOB) community structure and richness as an integrated part of soil functioning. This research aimed at investigating the effect of aboveground plant diversity on ammonia oxidizing bacteria diversity and function in forest and grassland soils with focus on the influence of (a) functional group identity of grassland plants (legumes, grasses, forbs), (b) grassland plant species richness and (c) tree species, on AOB diversity and function. Another objective of this research was to study the effect of a 3°C increase in air temperature on AOB diversity and function. The link between AOB diversity and function (potential nitrification) is also investigated. For grassland ecosystems, a microcosm experiment was realized. An experimental platform containing 288 assembled grassland communities was established in Wilrijk (Belgium). Grassland species were grown in 12 sunlit, climate controlled chambers. Each chamber contained 24 communities of variable species richness (S) (9 S=1, 9 S=3 and 6 S=9).The grassland species belonged to three functional groups: three species of each grasses (Dactylis glomerata L., Festuca arundinacea SCHREB., Lolium perenne L.), forbs (non-N-fixing dicots; Bellis perennis L., Rumex acetosa L., Plantagolanceolata L.), and legumes (N-fixing dicots; Trifolium repens L., Medicago sativa L., Lotus corniculatus L.). Half of these chambers were exposed to ambient temperature and the other half were exposed to (ambient +3°C) temperature. One ambient and one (ambient+3°C) chambers were destructively harvested 4, 16 and 28 months after the start of the experiment. The influence of plant functional group identity on the nitrification process and on AOB community structure and richness (AOB diversity) was assessed in soils collected from the first two destructive amplings (chapter 2). The effect of plant species richness on AOB diversity and function was considered for soils sampled after 16 and 28 months (chapter 3). AOB function was determined by potential nitrification. AOB community structure and richness were assessed by polymerase chain reaction followed by denaturing gradient gel electrophoresis (DGGE) and sequencing of excised DGGE bands. I found that functional group identity can affect AOB community structure. In particular, the presence of legumes, both in monoculture or in mixture with forbs and grasses, lead to AOB community composition changes towards AOB clusters tolerating higher ammonium concentrations. This change in AOB community structure was only linked to increased potential nitrification under monocultures of legumes, when ammonium was supposed to be not limiting. This study revealed that physiological attributes of AOB and resource availability may be important factors in controlling the nitrification process. This research showed that the impact of plant species richness on the nitrification process could be mediated by the interactions between plants and AOB, through competition for substrate. A 3°C increase in air temperature did not affect AOB community structure, richness or function. In forest ecosystems, we studied the effect of tree species in forest sites located in Belgian and in the Grand-Duchy of Luxembourg covered each by several deciduous or coniferous tree species (Fagus sylvatica L., Quercus petraea (Mattuschka) Lieblein, Picea abies (L.) Karst, Pseudotsuga menziesii (Mirbel) Franco). We investigated the influence of these tree species on microbial processes (chapter 5) related to C and N cycling, particularly with emphasize on the nitrification process and on the diversity of AOB (chapter 6). The results showed that the effect of tree species on net N mineralization was likely to be mediated through their effect on soil microbial biomass, reflecting their influence on organic matter content and carbon availability. Influence of tree species on nitrification (potential and relative) might be related to the presence of ground vegetation through its influence on soil ammonium and labile C availability. AOB community structure was more site-specific than tree specific. However, within sites, AOB community structure under broadleaved trees differed from the one under coniferous trees. The effect on tree species on AOB was likely to be driven by the influence of tree species on net N mineralization, which regulates the substrate availability for AOB. The results also demonstrated that the relationship between AOB diversity and function might be related both to AOB abundance and AOB community structure and richness. This thesis showed no clear relationship between AOB community structure or richness and AOB function. However, we revealed that aboveground grassland plant richness, grassland plant functional groups and tree species influence AOB community structure and richness. Actuellement, les écosystèmes sont soumis à dimportantes pressions anthropiques et environnementales, pouvant aboutir à des pertes massives de biodiversité. Les scientifiques sinterrogent sur limpact de ces perturbations sur la diversité et, par conséquent, sur lactivité des microorganismes du sol. En effet, ceux-ci régulent de nombreux processus du sol. Actuellement, de nombreuses lacunes subsistent dans la connaissance de la diversité microbienne du sol. Celles-ci peuvent être partiellement attribuées aux difficultés méthodologiques associées à l'étude des micro-organismes du sol. Lavènement des techniques moléculaires nous permet de combler ces lacunes. Les avancées réalisées dans l'étude des communautés microbiennes du sol ont mis en évidence le rôle crucial joué par les communautés microbiennes dans le fonctionnement des écosystèmes. De plus, il semblerait que les processus régulés par un groupe restreint dorganismes, tel le processus de nitrification, soient plus sensibles à toute altération de la communauté. Lobjectif de cette thèse était détudier la structure de la communauté ainsi que la richesse (nombre de bandes DGGE) des bactéries oxydant lammoniac (AOB) comme une partie intégrante du fonctionnement des sols. Notre étude se focalisait sur linfluence de (a) différents groupes fonctionnels de plantes (graminées, légumineuses, dicotylédones), (b) communautés de plantes présentant une richesse spécifique croissante et (c) différentes essences forestières, sur la diversité (structure de la communauté et richesse des AOB) et la fonction des AOB. Cette recherche étudiait également limpact dune augmentation de température de 3°C sur ces paramètres. Létablissement dun lien éventuel entre la diversité et la fonction (nitrification potentielle) des AOB a aussi été envisagé. Concernant les écosystèmes prairiaux, nous avons réalisé une étude en microcosmes. Une plateforme expérimentale comprenant 288 communautés artificielles de plantes a été établie à Wilrijk (Belgique). Cette plateforme consistait en 12 chambres, dont une moitié était à température ambiante et la seconde était à température ambiante augmentée de 3°C. Chaque chambre contient 24 communautés de plantes de richesse spécifique variable (9 S=1, 9 S=3 et 6 S=9). Les communautés de plantes sont créées avec 9 espèces de plantes appartenant à trois groupes fonctionnels : 3 espèces de graminées (Dactylis glomerata L., Festuca arundinacea SCHREB., Lolium perenne L.), de légumineuses (dicotylédones fixatrices dazote ;Trifolim repens L., Medicago sativa L., Lotus corniculatus L.), et de dicotylédones non fixatrices dazote (Bellis perennis L., Rumex acetosa L., Plantago lanceolata L.). Les sols issus dune chambre à température ambiante et dune chambre à température ambiante augmentée de 3°C ont été échantillonnés, respectivement, 4, 16 et 28 mois après le début de lexpérimentation. Linfluence des groupes fonctionnels de plantes sur le processus de nitrification ainsi que sur la structure de la communauté et la richesse des AOB a été mesuré sur les sols issus des deux premiers échantillonnages (chapitre 2). Nous avons mesuré leffet de la richesse croissante en plantes sur la diversité et lactivité des AOB sur les sols échantillonnés après 16 et 28 mois dexpérimentation (chapitre 3). La structure de la communauté ainsi que la richesse des AOB ont été évaluées à laide dune amplification spécifique par réaction de polymérisation en chaîne (PCR) de lADN génomique extrait du sol suivie par une séparation par électrophorèse sur gel dacrylamide en présence dun gradient dénaturant (DGGE). Nous avons identifié les différentes AOB présentes par séquençage des bandes DGGE excisées. Nos résultats ont montré que les différents groupes fonctionnels peuvent affecter la structure de la communauté des AOB. En particulier, la présence de légumineuses, aussi bien en monoculture quen mélange avec des graminées ou des dicotylédones non fixatrices dazote, provoque des changements au sein de la structure de la communauté des AOB, favorisant la présence de clusters tolérants des concentrations en ammonium plus élevées. Ces changements de la structure de la communauté des AOB sont liés à des augmentations de la production potentielle de nitrates (nitrification potentielle) quand lammonium est supposé être non limitant. Cette étude révèle que la physiologie des AOB ainsi que la disponibilité en substrat peuvent être des facteurs majeurs intervenant dans le contrôle du processus de nitrification. Cette recherche montre que linfluence de la richesse spécifique des plantes sur la nitrification pourrait dépendre des interactions entre les plantes et les AOB via la compétition pour le substrat. Une augmentation de la température de lair de 3°C na pas influencé les richesse, structure de la communauté ou les fonctions des AOB. Pour les écosystèmes forestiers, nous aborderons leffet de différentes essences forestières (Picea abies (L.) KARST, Fagus sylvatica L., Quercus petraea LIEBLEIN ; Pseudotsuga menziezii (MIRB.) FRANCO) dans différents peuplements au Grand Duché du Luxembourg et en Belgique. Nous avons étudié l'influence de ces essences forestières sur les processus microbiens (chapitre 5) liés aux cycles du carbone et de lazote, en particulier leur effet sur le processus de nitrification et la diversité des AOB (chapitre 6). Notre étude révèle que linfluence des essences forestières sur la minéralisation nette de lazote pourrait être attribuable à leur effet sur la biomasse microbienne, reflétant ainsi leur effet sur la teneur en matière organique et la disponibilité en carbone. Limpact des essences forestières sur la nitrification (à la fois sur la nitrification relative et sur la nitrification potentielle) serait conditionné par la présence de végétation au sol, en raison de linfluence de celle-ci sur la disponibilité en ammonium et en carbone labile. Nous avons observé que la structure de la communauté des AOB était plus spécifique aux sites quaux essences forestières. Cependant, au sein dun site, elle différait sous feuillus et sous conifères. Les essences forestières influenceraient la structure de la communauté des AOB au travers de limpact quelles ont sur la minéralisation nette de lazote qui régule, quant à elle, la disponibilité en ammonium. Cette recherche démontre que le lien observé entre la diversité et la fonction dépendrait la fois de labondance, de la structure de la communauté et de la richesse des AOB. Cette thèse na révélé aucune relation claire entre la structure de la communauté ou la richesse des AOB et leur fonction. Par contre, nous avons observé que la richesse spécifique et les groupes fonctionnels de plantes prairiales et les essences forestières affectent la structure de la communauté et la richesse des AOB.