No description available.

No description available.

The utilisation of fossil fuels for energy worldwide depletes the natural reserves and at the same time releases billions of tonnes of carbon dioxide and other greenhouse gases into the atmosphere. In order to reverse the negative effects of this accumulation, i.e., global warming and climatic changes, countries around the world are now considering nuclear energy and other cleaner sources of energy as a substitute to the burning of fossil fuels. The deployment of the later technology has progressed slowly due to lack of public support. The general public and environmental lobbyists worry about the discharge of radioactive waste from nuclear power generation and accidents that have occurred in the nuclear power industry in the recent past. One of pollutants of concern is uranium which is discharged from the nuclear generation processes as the highly toxic uranium-6, (U(VI)). U(VI) coming from the reactors is radioactive as well as highly toxic to aquatic life forms. Biological treatment of metal pollutants is viewed as an environmentally friendly alternative to conventional physical/chemical treatment methods, especially in dilute solutions where physical/chemical methods may not be effective. Microbial processes may be applied both as in situ and/or ex situ processes. Microbial consortia, consisting of several species of microorganisms in the form of bioflocs for reducing/removing the pollutants have been used as they preserve the complex interrelationships that exist between species in the source. The results of this study demonstrate the potential of microbial U(VI) reduction as a possible replacement technology for physical/chemical processes currently in use in the nuclear industry. A detailed analysis of the biological reduction of uranium-(VI) was conducted and the following were the main findings of the study: (1) Background uranium concentration in soil from the mine was determined to be 168 mg/kg, a very high value compared to the typical concentration of uranium in natural soils; (2) Among six bacteria species isolated from a uranium mine in Limpopo, South Africa, three anaerobic species – Pantoea sp., Enterobacter sp. and Pseudomonas stutzeri – reduced U(VI) to U(VI) and facilitated the removal of the uranium species from solution. Based on batch studies and cell disruption studies, the laws governing microbial U(VI) reduction were determined and the kinetic parameters for U(VI) reduction were determined. The cultures in this study reduced uranium-U(VI) at a rate better than rates found in literature for other microorganisms. Reduction rates reported in this paper can be used to assess the applicability of bioreduction for uranium removal processes. / Dissertation (MSc)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

Microaerobic fermentation (MF) is a process of controlled degradation of organic waste material that occurs in enclosed fermentors under micro-aerobic conditions at near-room temperature. MF processing of vegetal materials progresses to endpoints in about 2-5 weeks. During MF processing, an acidic leachate rich in organic acids and alcohols is produced. The research presented in this thesis focuses on the efficiency of MF pre-processing of feedstock containing fibrous lignocellulosic (FLC) materials; efficiency of microbial and insect larvae-based treatments of MF leachate; tolerance of the Black Soldier fly larvae (BSFL) to various biological inhibitors common in leachate; and effectiveness of using MF and BSFL solid and liquid processing products as agricultural fertilizers. Results indicate that MF is unsuitable for pre-processing of FLC materials. Enhanced MF leachate treatment may increase efficiency of FLC processing though. Leachate can be efficiently treated using BSFL which decrease overall leachate toxicity. BSFL are able to tolerate increased levels of many of the biological inhibitors within the leachate including ethanol, acetate, pH extremes and temperature. MF solid residues increased corn plant growth when amended into soil, but residues resulting from BSFL processing of solid organics stunted corn plant growth. Short-term phytotoxicity of MF leachate was eliminated by diluting it 10 - 10,000 times or through BSFL processing. It can be concluded that MF processing of organics is beneficial for producing solid soil amendments from non-FLC materials and that dilution or BSFL treatment of MF leachate leads to a beneficial liquid fertilizer.

This study was carried out to develop combined cultures which were composed of anaerobic and aerobic cultures, and could survive and operate under alternating aerobic and/or microaerobic / anaerobic conditions in semi-continuous and Upflow Sludge Blanket (USB) reactors. Granular combined cultures with median diameter of 1.28-1.86 mm and 0.8 mm were developed from suspended anaerobic and aerobic cultures in semi-continuous and USB reactors, respectively. Significant specific methanogenic activity (SMA, 14-42 mL CH4/g VSS.hr) and specific oxygen uptake rate (SOUR, 6-47 mg DO/g VSS.hr) values of combined granules in semi-continuous reactors were comparable to those of anaerobic and aerobic granules. Similarly, combined granules in USB reactors exhibited noteworthy SMA and SOUR values of 11-77 mL CH4/g VSS.hr and 10-75 mg DO/g VSS.hr, respectively. Combined granules developed in semi-continuous reactors were found to overcome the drawbacks of both anaerobic and aerobic granules such as the need for long start-up and low stability, respectively. Combined cultures were also developed from anaerobic granular and suspended aerobic cultures in three USB reactors aerated at 10 mL air/min for 4 hours/day (R2), every other day (R3) and 24 hours/day (R4). The use of combined cultures was found to be advantageous compared to the anaerobic granules for the treatment of low strength wastewaters. During municipal wastewater treatment at influent 5-day biochemical oxygen demand (BOD5) concentration of 53-118 mg/L (Hydraulic retention time, HRT: 0.75 day), combined cultures in R2, R3 and R4 exhibited average BOD5 removal efficiencies of 52, 75 and 76%, respectively. Combined granules developed in USB reactor also displayed significant BOD5 removal efficiencies (66-68%) during municipal wastewater application (HRT: 0.75 day). Combined cultures/granules developed in USB reactors might be proposed as an alternative for municipal wastewater treatment due to their advantages such as achievement of required discharge standards, prevention of biomass loss / settleability problems unlike activated sludge systems and possible methanogenic activity as well as high settling characteristics comparable to those of anaerobic granules.

Submitted by Jean Medeiros (jeanletras@uepb.edu.br) on 2017-08-11T13:35:45Z No. of bitstreams: 1 PDF - Rodrigo de Andrade Barbosa.pdf: 16832850 bytes, checksum: 003b948634b5b9d73fdf0e982252cd69 (MD5) / Made available in DSpace on 2017-08-11T13:35:45Z (GMT). No. of bitstreams: 1 PDF - Rodrigo de Andrade Barbosa.pdf: 16832850 bytes, checksum: 003b948634b5b9d73fdf0e982252cd69 (MD5) Previous issue date: 2017-04-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the treatment of sanitary sewage in UASB reactors anaerobic digestion occurs, among the several processes that comprise it, sulfide produces sulfide, which causes several problems, such as: odor emanation, corrosion, toxicity and decrease of methane concentration in the Biogas. This research aims to improve processes to produce elemental sulfur and reduce the concentration of sulfides in the effluent and biogas of UASB reactors with the addition of oxidants in the treatment of sanitary sewage. The experimental investigation was divided into three phases. In the first one, three reactors were used, two microaerobes and a UASB reactor with addition of nitrate to the tributary. In the second phase, a microaerobic reactor and a UASB reactor with nitrate addition were operated. In the third phase two reactors were operated, one microaerobic and one UASB reactor (control). When analyzing the results of the reactor monitoring, it was possible to identify that the first-stage microaerobic reactors with sulfide removal efficiencies higher than 90%. And an elemental sulfur production of approximately 28% in relation to the total affluent sulfur. In the second phase the reactors also removed more than 90% of the total dissolved sulfide, but with respect to the elemental sulfur, the production had less expressive results. The nitrate addition reactors showed 98% of the sulphide removal 2- -1 efficiencies, with a mean concentration of 0.2 ± 0.06 mg S-S . L . In the third phase the microaeration provided a sulfide removal of 84% in the effluent and 97% in the biogas, with an average of 8 ppm. Then there was a reduction in the emanation of odors and several other problems related to high concentrations of sulphide in the effluent and in the biogas of UASB reactors. / No tratamento de esgoto sanitário em reatores UASB ocorre a digestão anaeróbia, dentre os vários processos que a compõem, a sulfetogênese ocasiona a produção de sulfetos, que acarreta vários problemas, como: emanação de odores, corrosão, toxicidade e diminuição da concentração de metano no biogás. Esta pesquisa tem como objetivo aprimorar processos para produzir enxofre elementar e reduzir a concentração de sulfetos no efluente e no biogás de reatores UASB com adição de oxidantes, no tratamento de esgoto sanitário. A investigação experimental foi dividida em três fases. Na primeira foram utilizados 3 reatores, dois microaeróbios e um reator UASB com adição de nitrato ao afluente. Na segunda fase foram operados um reator microaeróbio e um reator UASB com adição de nitrato. Na terceira fase foram operados dois reatores, um microaeróbio e um reator UASB (controle). Ao se analisar os resultados do monitoramento dos reatores, foi possível identificar que os reatores microaeróbios operados na primeira fase com eficiências de remoção de sulfeto superiores a 90%. E uma produção de enxofre elementar de aproximadamente 28% em relação ao enxofre total afluente. Na segunda fase os reatores também removeram mais de 90% do sulfeto total dissolvido, porém referente ao enxofre elementar, a produção teve resultados menos expressivos. Os reatores com adição de nitrato foram observados 98% de eficiências na remoção de 2- -1 sulfetos, com concentração média de 0,2 ± 0,06 mg S-S . L . Na Terceira fase a microaeração proporcionou uma remoção de sulfetos de 84% no efluente e de 97% no biogás, com média de 8 ppm. Então houve uma redução na emanação de odores e diversos outros problemas relacionados a concentrações elevadas de sulfeto no efluente e no biogás de reatores UASB.

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior / O presente estudo teve o objetivo de avaliar o uso de reatores biolÃgicos, sob condiÃÃes anaerÃbias e microaerÃbias, como opÃÃo de biorremediaÃÃo ex situ de Ãguas contaminadas com BTEX. Inicialmente, foi desenvolvido, otimizado e validado um mÃtodo analÃtico para a detecÃÃo e quantificaÃÃo de BTEX em Ãguas e efluentes, o qual consistia em extraÃÃo por headspace seguida de cromatografia gasosa com detecÃÃo por fotoionizaÃÃo. Posteriormente, foram conduzidos experimentos em fluxo contÃnuo em dois reatores anaerÃbios mesofÃlicos (27 ÂC) â um deles operado sob condiÃÃes metanogÃnicas e, em seguida, sob condiÃÃes microaerÃbias, e o outro, apenas sob condiÃÃes sulfetogÃnicas â a fim de verificar a melhor condiÃÃo operacional para a remoÃÃo de BTEX. Os reatores foram alimentados com Ãgua contaminada com BTEX (~3 mgÂL-1 de cada composto) e etanol (co-substrato), e, dependendo da condiÃÃo redox avaliada, investigou-se o efeito de diferentes parÃmetros operacionais, tais como tempo de detenÃÃo hidrÃulica (24, 36 e 48 h), recirculaÃÃo de efluente, concentraÃÃo de co-substrato, relaÃÃo DQO/SO4 2- e microaeraÃÃo, no desempenho de remoÃÃo de BTEX. AlÃm disso, o reator metanogÃnico sob condiÃÃes microaerÃbias foi submetido a simulaÃÃes de choques de carga e de ausÃncia desses compostos, e de falhas operacionais, como desligamento do sistema e desligamento da microaeraÃÃo, para verificaÃÃo de sua robustez. Sob condiÃÃes metanogÃnicas, dependendo do composto, as eficiÃncias de remoÃÃo variaram de 38 a 97%. PorÃm, o aumento da carga aplicada de BTEX, em consequÃncia da reduÃÃo do tempo de detenÃÃo hidrÃulica de 48 para 24 h, parece ter afetado negativamente o processo de remoÃÃo. Ainda sob condiÃÃes metanogÃnicas, tambÃm se verificou o efeito da recirculaÃÃo de efluente na remoÃÃo de BTEX para altas e baixas concentraÃÃes de co-substrato (etanol). Quando altas concentraÃÃes de etanol foram utilizadas, o impacto da recirculaÃÃo de efluente nÃo foi evidente, jà que, provavelmente, a elevada produÃÃo de biogÃs teria sido suficiente para garantir uma transferÃncia de massa efetiva. Sob condiÃÃes sulfetogÃnicas, a adiÃÃo de sulfato em diversas relaÃÃes DQO/SO4 2- nÃo alterou a remoÃÃo de BTEX, sugerindo que as bactÃrias redutoras de sulfato nÃo estariam diretamente relacionadas à ativaÃÃo inicial dos compostos aromÃticos. Sob condiÃÃes microaerÃbias, elevadas eficiÃncias de remoÃÃo de BTEX foram alcanÃadas (> 90%). à provÃvel que a adiÃÃo de baixas concentraÃÃes de oxigÃnio tenha facilitado a ativaÃÃo inicial dos compostos BTEX, a qual à considerada a etapa limitante do processo de degradaÃÃo anaerÃbia, principalmente para o benzeno. Ainda, constatou-se que a presenÃa de altas concentraÃÃes de etanol afetou negativamente a remoÃÃo de BTEX, notadamente para o benzeno, sob as diferentes condiÃÃes redox testadas, jà que à um substrato preferencialmente degradÃvel em relaÃÃo aos compostos aromÃticos. Finalmente, com relaÃÃo à robustez do reator metanogÃnico sob condiÃÃes microaerÃbias, o sistema conseguiu lidar com os choques de carga de BTEX embora choques consecutivos tenham aumentado seu tempo de recuperaÃÃo. O perÃodo de ausÃncia de BTEX parece ter prejudicado a microbiota do reator, pois a qualidade do efluente deteriorou-se consideravelmente apÃs reintroduÃÃo dos compostos. O desligamento da microaeraÃÃo impactou negativamente a remoÃÃo de BTEX, mas o sistema recuperou-se rapidamente apÃs restabelecimento das condiÃÃes microaerÃbias. / The present study aimed to evaluate the use of biological reactors under anaerobic and microaerobic conditions, as an option of ex situ bioremediation of BTEX-contaminated waters. Initially, an analytical method for BTEX detection and quantification in waters and wastewaters, which consisted of headspace extraction followed by gas chromatography with detection by photoionization, was developed, optimized and validated. Subsequently, continuous-flow experiments were conducted in two mesophilic (27 ÂC) anaerobic reactors â one of them operated under methanogenic conditions and, afterwards, under microaerobic conditions, and the other one only under sulfidogenic conditions â a in order to determine the best operational condition for BTEX removal. The reactors were fed with water contaminated with BTEX (~3 mgÂL-1 of each compound) and ethanol (co-substrate), and, depending on the redox condition evaluated, the effect of some operational parameters, such as hydraulic retention time (24, 36 and 48 h), effluent recirculation, co-substrate concentration, DQO/SO4 2- ratio and microaeration, was investigated in BTEX removal performance. Furthermore, the methanogenic reactor under microaerobic conditions was submitted to simulated situations of shock loading and absence of these compounds, and operational failures, such as system and microaeration shutdown to assess its robustness. Under methanogenic conditions, depending on the compound, removal efficiencies ranged from 38 to 97%. However, the increase of applied BTEX load, as a consequence of hydraulic detention time reduction from 48 to 24 h, seems to have adversely affected the removal process. Moreover, under methanogenic conditions, the effluent recirculation effect on BTEX removal was also assessed when high and low co-substrate (ethanol) concentrations were applied. For high ethanol concentrations, the impact of effluent recirculation was not evident since, probably, the high biogas production would have been sufficient to ensure effective mass transfer. Under sulfidogenic conditions, sulfate addition at different DQO/SO4 2- ratios did not change BTEX removal, which suggests sulfate-reducing bacteria would not be directly related to initial activation of aromatic compounds. Under microaerobic conditions, high BTEX removal efficiencies were achieved (> 90%). It is likely the addition of low oxygen concentrations has facilitated the initial activation of BTEX compounds, which is considered the limiting step of the anaerobic degradation process, mainly for benzene. Furthermore, the presence of high ethanol concentrations negatively affected BTEX removal, particularly for benzene, under the different redox conditions tested, since it is a preferentially degradable substrate when compared to the aromatic compounds. Finally, regarding the methanogenic reactor robustness under microaerobic conditions, the system could cope with BTEX load shocks although consecutive shocks have increased its recovery time. The period of BTEX absence seems to have negatively affected the reactor microbiota because the effluent quality deteriorated considerably after compounds reintroduction. The microaeration shutdown also negatively impacted the removal of BTEX, but the system recovered quickly after microaerobic conditions reestablishment.

No description available.

L’atmosphère terrestre est très riche en azote (N2). Mais cet azote diatomique est sous une forme très stable, inutilisable par la majorité des êtres vivants malgré qu’il soit indispensable pour la synthèse de matériels organiques. Seuls les procaryotes diazotrophiques sont capables de vivre avec le N2 comme source d’azote. La fixation d’azote est un processus qui permet de produire des substances aminées à partir de l’azote gazeux présent dans l’atmosphère (78%). Cependant, ce processus est très complexe et nécessite la biosynthèse d’une vingtaine de protéines et la consommation de beaucoup d’énergie (16 molécules d’ATP par mole de N2 fixé). C’est la raison pour laquelle ce phénomène est rigoureusement régulé. Les bactéries photosynthétiques pourpres non-sulfureuses sont connues pour leur capacité de faire la fixation de l’azote. Les études faites à la lumière, dans le mode de croissance préféré de ces bactéries (photosynthèse anaérobie), ont montré que la nitrogénase (enzyme responsable de la fixation du diazote) est sujet d’une régulation à trois niveaux: une régulation transcriptionnelle de NifA (protéine activatrice de la transcription des gènes nif), une régulation post-traductionnelle de l’activité de NifA envers l’activation de la transcription des autres gènes nif, et la régulation post-traductionnelle de l’activité de la nitrogénase quand les cellules sont soumises à un choc d’ammoniaque. Le système de régulation déjà décrit fait intervenir essentiellement une protéine membranaire, AmtB, et les deux protéines PII, GlnB et GlnK. Il est connu depuis long temps que la nitrogénase est aussi régulée quand une culture photosynthétique est exposée à la noirceur, mais jusqu’aujourd’hui, on ignore encore la nature des systèmes intervenants dans cette régulation. Ainsi, parmi les questions qui peuvent se poser: quelles sont les protéines qui interviennent dans l’inactivation de la nitrogénase lorsqu’une culture anaérobie est placée à la noirceur? Une analyse de plusieurs souches mutantes, amtB- , glnK- , glnB- et amtY- poussées dans différentes conditions de limitation en azote, serait une façon pour répondre à ces interrogations. Alors, avec le suivi de l’activité de la nitrogénase et le Western Blot, on a montré que le choc de noirceur provoquerait un "Switch-off" de l’activité de la nitrogénase dû à une ADP-ribosylation de la protéine Fe. On a réussit aussi à montrer que ii tout le système déjà impliqué dans la réponse à un choc d’ammoniaque, est également nécessaire pour une réponse à un manque de lumière ou d’énergie (les protéines AmtB, GlnK, GlnB, DraG, DraT et AmtY). Or, Rhodobacter capsulatus est capable de fixer l’azote et de croitre aussi bien dans la micro-aérobie à la noirceur que dans des conditions de photosynthèse anaérobies, mais jusqu'à maintenant sa régulation dans l’obscurité est peu étudiée. L’étude de la fixation d’azote à la noirceur nous a permis de montrer que le complexe membranaire Rnf n’est pas nécessaire à la croissance de R. capsulatus dans de telles conditions. Dans le but de développer une façon d’étudier la régulation de la croissance dans ce mode, on a tout d’abord essayé d’identifier les conditions opératoires (O2, [NH4 + ]) permettant à R. capsulatus de fixer l’azote en microaérobie. L’optimisation de cette croissance a montré que la concentration optimale d’oxygène nécessaire est de 10% mélangé avec de l’azote. / The atmosphere of the Earth is very rich in nitrogen (N2). However, diatomic nitrogen is very stable and therefore unusable by the majority of life forms even though it is necessary for the synthesis of a variety of organic compounds. Only diazotrophic procaryotes are capable of using N2 as nitrogen source. Their nitrogen fixation allows the production of aminated compounds from atmospheric nitrogen (78 %). However, this process is very complex and requires the biosynthesis of about twenty proteins and the consumption of a lot of energy (16 molecules of ATP per molecule of N2 fixed), thus necessitating its tight regulation. The purple non-sulfur photosynthetic bacteria are known for their ability to carry out nitrogen fixation. Studies conducted in the light, the preferred mode of growth of these bacteria (anaerobic photosynthetic), have shown that nitrogenase (the enzyme responsible for dinitrogen fixation) is subject to regulation at three levels: transcriptional regulation of NifA (activator protein for the transcription of nif genes), posttranslational regulation of the activity of NifA to activate nif gene transcription, and posttranslational regulation of nitrogenase activity when cells are subjected to an ammonium shock. The control system already described involves essentially a membrane protein, AmtB and both PII proteins, GlnK and GlnB. It has long been known that nitrogenase is regulated when light is suddenly removed from a culture, but until now it is unclear whether these systems are also involved in the regulation of nitrogen fixation in dark. Thus, one outstanding question is what are the proteins involved in the inactivation of nitrogenase when a light-grown culture is placed in the dark? An analysis of several mutant strains; amtB-, glnK-, glnB-, and amtY- under different conditions of nitrogen deficiency was used to address this question. Using measurements of nitrogenase activity and Fe protein modification by Western blotting, we were able to show that darkness causes a "switch-off” of nitrogenase due to ADP- ribosylation of Fe protein. Thus, the system that has already been described as involved in the response to a lack of ammonia, is also required for a response to a lack of light or energy (AmtB, GlnK, GlnB, DraG, and DraT, and AmtY). However, Rhodobacter capsulatus is also able to fix nitrogen and grow micro-aerobically in the dark as well as photosynthetically under anaerobic conditions, but so far its regulation in the dark has been little studied. The study of nitrogen fixation in the dark allowed us to show that the Rnf membrane complex is not required for growth of R. capsulatus in such conditions. In order to develop a way to study its regulation during this growth mode, we have attempted to identify the operating conditions (O2, [NH4+]), allowing R. capsulatus to fix nitrogen micro-aerobically. The optimization of this conditions has shown that the optimal concentration of oxygen required is 10% mixed with nitrogen.

L’atmosphère terrestre est très riche en azote (N2). Mais cet azote diatomique est sous une forme très stable, inutilisable par la majorité des êtres vivants malgré qu’il soit indispensable pour la synthèse de matériels organiques. Seuls les procaryotes diazotrophiques sont capables de vivre avec le N2 comme source d’azote. La fixation d’azote est un processus qui permet de produire des substances aminées à partir de l’azote gazeux présent dans l’atmosphère (78%). Cependant, ce processus est très complexe et nécessite la biosynthèse d’une vingtaine de protéines et la consommation de beaucoup d’énergie (16 molécules d’ATP par mole de N2 fixé). C’est la raison pour laquelle ce phénomène est rigoureusement régulé. Les bactéries photosynthétiques pourpres non-sulfureuses sont connues pour leur capacité de faire la fixation de l’azote. Les études faites à la lumière, dans le mode de croissance préféré de ces bactéries (photosynthèse anaérobie), ont montré que la nitrogénase (enzyme responsable de la fixation du diazote) est sujet d’une régulation à trois niveaux: une régulation transcriptionnelle de NifA (protéine activatrice de la transcription des gènes nif), une régulation post-traductionnelle de l’activité de NifA envers l’activation de la transcription des autres gènes nif, et la régulation post-traductionnelle de l’activité de la nitrogénase quand les cellules sont soumises à un choc d’ammoniaque. Le système de régulation déjà décrit fait intervenir essentiellement une protéine membranaire, AmtB, et les deux protéines PII, GlnB et GlnK. Il est connu depuis long temps que la nitrogénase est aussi régulée quand une culture photosynthétique est exposée à la noirceur, mais jusqu’aujourd’hui, on ignore encore la nature des systèmes intervenants dans cette régulation. Ainsi, parmi les questions qui peuvent se poser: quelles sont les protéines qui interviennent dans l’inactivation de la nitrogénase lorsqu’une culture anaérobie est placée à la noirceur? Une analyse de plusieurs souches mutantes, amtB- , glnK- , glnB- et amtY- poussées dans différentes conditions de limitation en azote, serait une façon pour répondre à ces interrogations. Alors, avec le suivi de l’activité de la nitrogénase et le Western Blot, on a montré que le choc de noirceur provoquerait un "Switch-off" de l’activité de la nitrogénase dû à une ADP-ribosylation de la protéine Fe. On a réussit aussi à montrer que ii tout le système déjà impliqué dans la réponse à un choc d’ammoniaque, est également nécessaire pour une réponse à un manque de lumière ou d’énergie (les protéines AmtB, GlnK, GlnB, DraG, DraT et AmtY). Or, Rhodobacter capsulatus est capable de fixer l’azote et de croitre aussi bien dans la micro-aérobie à la noirceur que dans des conditions de photosynthèse anaérobies, mais jusqu'à maintenant sa régulation dans l’obscurité est peu étudiée. L’étude de la fixation d’azote à la noirceur nous a permis de montrer que le complexe membranaire Rnf n’est pas nécessaire à la croissance de R. capsulatus dans de telles conditions. Dans le but de développer une façon d’étudier la régulation de la croissance dans ce mode, on a tout d’abord essayé d’identifier les conditions opératoires (O2, [NH4 + ]) permettant à R. capsulatus de fixer l’azote en microaérobie. L’optimisation de cette croissance a montré que la concentration optimale d’oxygène nécessaire est de 10% mélangé avec de l’azote. / The atmosphere of the Earth is very rich in nitrogen (N2). However, diatomic nitrogen is very stable and therefore unusable by the majority of life forms even though it is necessary for the synthesis of a variety of organic compounds. Only diazotrophic procaryotes are capable of using N2 as nitrogen source. Their nitrogen fixation allows the production of aminated compounds from atmospheric nitrogen (78 %). However, this process is very complex and requires the biosynthesis of about twenty proteins and the consumption of a lot of energy (16 molecules of ATP per molecule of N2 fixed), thus necessitating its tight regulation. The purple non-sulfur photosynthetic bacteria are known for their ability to carry out nitrogen fixation. Studies conducted in the light, the preferred mode of growth of these bacteria (anaerobic photosynthetic), have shown that nitrogenase (the enzyme responsible for dinitrogen fixation) is subject to regulation at three levels: transcriptional regulation of NifA (activator protein for the transcription of nif genes), posttranslational regulation of the activity of NifA to activate nif gene transcription, and posttranslational regulation of nitrogenase activity when cells are subjected to an ammonium shock. The control system already described involves essentially a membrane protein, AmtB and both PII proteins, GlnK and GlnB. It has long been known that nitrogenase is regulated when light is suddenly removed from a culture, but until now it is unclear whether these systems are also involved in the regulation of nitrogen fixation in dark. Thus, one outstanding question is what are the proteins involved in the inactivation of nitrogenase when a light-grown culture is placed in the dark? An analysis of several mutant strains; amtB-, glnK-, glnB-, and amtY- under different conditions of nitrogen deficiency was used to address this question. Using measurements of nitrogenase activity and Fe protein modification by Western blotting, we were able to show that darkness causes a "switch-off” of nitrogenase due to ADP- ribosylation of Fe protein. Thus, the system that has already been described as involved in the response to a lack of ammonia, is also required for a response to a lack of light or energy (AmtB, GlnK, GlnB, DraG, and DraT, and AmtY). However, Rhodobacter capsulatus is also able to fix nitrogen and grow micro-aerobically in the dark as well as photosynthetically under anaerobic conditions, but so far its regulation in the dark has been little studied. The study of nitrogen fixation in the dark allowed us to show that the Rnf membrane complex is not required for growth of R. capsulatus in such conditions. In order to develop a way to study its regulation during this growth mode, we have attempted to identify the operating conditions (O2, [NH4+]), allowing R. capsulatus to fix nitrogen micro-aerobically. The optimization of this conditions has shown that the optimal concentration of oxygen required is 10% mixed with nitrogen.