La presente tesis está enmarcada en el desarrollo de los sistemas de soporte de vida biológicos, de especial aplicación para los viajes espaciales tripulados de larga duración.Concretamente, este trabajo se centra en el estudio, análisis, modelización y escalado de uno de los cinco compartimentos que integran el bucle MELiSSA, el compartimento fotoheterotrófico. Los experimentos han sido encaminados a determinar la influencia de la naturaleza de la radiación, de la irradiancia incidente y de la naturaleza y concentración de la fuente de carbono sobre la velocidad de crecimiento de las células de R. rubrum. También se ha analizado las consecuencias del cambio de escala del fotobiorreactor, observando la particular influencia de las condiciones ambientales en la composición y en el crecimiento de las células de R. rubrum.La información experimental obtenida ha servido para la construcción de un modelo que predice el crecimiento de las células en función de la concentración de fuente de carbono y de la cantidad de radiación subministrada. En una primera fase se calcula el perfil de irradiancia en el interior del cultivo en función de la irradiancia incidente, de la concentración de células y de las dimensiones del fotobiorreactor, y después este perfil es utilizado para determinar la velocidad de crecimiento de las células teniendo también en consideración las condiciones de cultivo.Asimismo, el modelo se ha utilizado como una herramienta para el dimensionado del fotobiorreactor piloto a una escala suficiente para conseguir los objetivos de demostración fijados en el Proyecto MELiSSA.Finalmente, se ha diseñado el fotobiorreactor a escala piloto, así como todos los equipos auxiliares necesarios (depósitos pulmones, válvulas, sondas, circuito de esterilización, lazos de control, caudalímetros, etc.) para la operación del compartimento en condiciones estériles durante largos periodos de tiempo. / The present thesis is developed in the mark of the development of biological support systems for the long-term space manned missions.Specifically, this study is centred in the analysis and scale-up of one of the five compartments that integrate the MELiSSA loop, the photoheterotrophic compartment. The experiments have been designed to determine the influence of the nature of the radiation, the incident irradiance and the nature and concentration of the carbon source on the growth rate of R. rubrum cells. Moreover, it has been studied the consequences of the scale-up of the photobiorreactor and it has been observed that the influence of the environmental conditions in the composition and the growth rate of R. rubrum cells is a key factor.The experimental data obtained has been used for the construction of a model, which is developed, calibrated and validated in this thesis. The model predicts the growth of the cells based on two parameters: the concentration of carbon source in the culture and the amount of radiation supplied. In a first step, the profile of irradiance inside the culture is calculated, which depends on the concentration of cells and the dimensions of the fotobiorreactor. Then, in a second step, the profile of irradiance is used to determine the cells growth rate. Moreover, the model has been used as a tool for the sizing of the fotobiorreactor at pilot scale. And, finally, the pilot fotobiorreactor has been designed, as well as all of the auxiliary equipment that is needed (buffer tanks, valves, sensors, circuit of sterilization, control loops, mass flowmeters, etc.) for the operation of the photobiorreactor in sterile conditions during long periods of time.

Stuttgart, Univ., Diss., 2003.

Stuttgart, Univ., Diplomarbeit, 2006.

Adaptability is one of the reasons for the success of bacteria, allowing them to survive in conditions where no other organisms would be able to thrive. Nitrogen deficiency, for example, can be a limiting factor for the growth of micro-organisms, as this element is an essential part of almost all types of biomolecules. As such, some bacteria have evolved specific mechanisms to overcome nitrogen limitation. Nitrogen fixing bacteria, or diazotrophs, use a specific enzyme complex, nitrogenase, in order to harness this element from the enormous reservoir that is the Earth’s atmosphere. However, nitrogen fixation is a demanding process for the cells, requiring vast amounts of energy and tight regulation. In this thesis we explore the mechanisms regulating nitrogen fixation in Rhodospirillum rubrum, a purple non-sulphur photosynthetic bacterium. Using proteomics tools, we show how the regulation of both the nitrogen and carbon fixation processes is interconnected, possibly in order to maintain the intracellular redox balance. Using a new detergent molecule, we also demonstrate how nitrogen availability affects the chromatophore membrane proteome. Our studies have revealed the crucial role of the cellular pool of 2-oxoglutarate (2OG) for adequate signaling through the PII proteins and the effects resulting from artificially manipulating this metabolite’s concentration. In R. rubrum nitrogenase is also subjected to post-translational control (the “switch-off” effect) and this work shows for the first time that the enzyme modifying nitrogenase (Dinitrogenase Reductase ADP-ribsosyl Transferase or DRAT) forms a complex with the PII protein GlnB. This complex allows DRAT activation and its formation – and, therefore, DRAT activity – is regulated by binding of ADP:ATP and 2OG to GlnB. Upon light withdrawal, nitrogenase activity anaerobically in the dark is also here demonstrated to be dependent on the activity of the pathway starting in pyruvate formate-lyase and we show how different nitrogen sources influence the switch-off response. This response can, in some conditions, be modified by addition of pyruvate and we have studied how this metabolite influences nitrogenase activity and switch-off regulation. This study allows a better understanding of the underlying processes controlling the metabolic routes in R. rubrum and also provides new insights into regulation of enzyme activity, paving the road for the complete establishment of the mechanisms regulating nitrogenase switch-off. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: In press. Paper 3: Submitted. Paper 4: Manuscript. Paper 5: Submitted.</p>