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Altres ajuts: acords transformatius de la UAB Life support systems (LSSs) are autonomous systems integrating various generation, recycling, and consumption subsystems with storage capability to maintain the balance of key system compounds. A novel hierarchical control is proposed in this paper to operate an exemplary controlled ecological LSS. The study focuses on the control of O concentration in the crew compartment, as the main consumer of a LSS, while coordinating a network of biological compartments with a variety of generation, consumption, and storage capabilities. A concentrated gas buffer tank is included in the system to demonstrate its capability to support the system operation flexibility and efficiency. Simulation analyses for changing O demand scenarios are carried to assess the proposed control architecture performance.

limnospira indica pcc8005 growth in photobioreactor2020-11-25; International audience; the arthrospira-b experiment is the first experiment in space ever allowing the online measurements of both oxygen production rate and growth rate of limnospira indica pcc8005 in batch photobioreactors running on-board iss. four bioreactors were integrated in the iss biolab facility. each reactor was composed of two chambers (gas and liquid) separated by a ptfe membrane and was run in batch conditions. oxygen production was monitored by online measurement of the total pressure increase in the gas chamber. the experiments are composed of several successive batch cultures for each reactor, performed in parallel on iss and on ground. in this work, a model for the growth of the cyanobacterium limnospira indica pcc8005 (also known as arthrospira or spirulina) in these space membrane photobioreactors was proposed and the simulation results obtained are compared to the experimental results gathered in space and on ground. the photobioreactor model was based on a light transfer limitation model, already used to describe and predict the growth and oxygen production in small to large scale ground photobioreactors. it was completed by a model for ph prediction in the liquid phase allowing assessment of the ph increase associated to the bicarbonate consumption for the biomass growth. a membrane gas-liquid transfer model is used to predict the gas pressure increase in the gas chamber. substrate limitation is considered in the biological model. a quite satisfactory fit was achieved between experimental and simulation results when a suitable mixing of the liquid phase was maintained. the data showed that microgravity has no first order effect on the oxygen production rate of limnospira indica pcc8005 in a photobioreactor operating in space in zero gravity conditions.

Acetic acid is one of the major potential inhibitors of cellular growth resulting from acid pretreatment of lignocellulosic biomass. To use lignocellulose hydrolysate in biorefineries it is necessary to assess their effect on the microorganisms likely to be used. An attractive option is to use a part of these hydrolysates for on-site cellulase production. Based on an industrial process that included a fast initial growth phase, the effect on Trichoderma reesei grown on glucose was assessed and modeled at different concentrations and pH. Acetic acid had a strong effect on T. reesei growth rate and yield, which correlated only with the concentration of the undissociated form in solution. The specific growth rate was accurately modeled by two different classic inhibition models as a function of pH and total acetic acid concentration. Co-consumption of glucose and acetic acid was observed, so that the culture medium was gradually detoxified by the cells. With or without glucose, acetic acid was miner...

Inspired by a terrestrial ecosystem, Micro-Ecological Life Support System Alternative (MELiSSA) is a project focused on a closed-loop life support system intended for future long-term manned missions (Moon and Mars bases). Started by the ESA in 1989, this 5-compartment concept has evolved through a mechanistic engineering approach designed to acquire both theoretical and technical knowledge. In its current state of development, the project can now start to demonstrate the MELiSSA loop concept at pilot scale. Thus, an integration strategy for a MELiSSA Pilot Plant (MPP) has been defined, describing the different test phases and connections between compartments. The integration steps are due to be started in 2008 and completed with a complete operational loop in 2015. The ultimate objective is to achieve a closed liquid and gas loop fulfiling 100% of oxygen requirements and at least 20% of food requirements for one-man. Although the integration logic could start with the most advanced processes in terms of knowledge and hardware development, this logic needs to be expanded to encompass a high-level simulation policy. This simulation exercise will make it possible to run effective demonstrations of each independent process, followed by progressive coupling with other processes in operational conditions mirroring as far as possible the final configuration. The theoretical approach described in this paper is based on mass balance models of each MELiSSA compartment which are used to simulate each integration step and the complete MPP loop itself. These simulations will help identify criticalities in each integration step and check consistency between objectives, flows, recycling efficiencies and sizing of the pilot reactors. An MPP scenario compatible with current knowledge on the operation of the pilot reactors was investigated, and the theoretical performances of the system were compared against the objectives assigned to the MPP. This scenario makes it possible to highlight the most important integration milestones and simulate their behaviour.

Space exploration programmes, currently under discussion in the US and in Europe, foresee human missions to Mars to happen within the first half of this century. In this context, the European Space Agency (ESA) has conducted a study on the human responses, limits and needs for such exploratory missions, the so-called HUMEX study (ESA SP-1264). Based on a critical assessment of the limiting factors for human health and performance and the definition of the life science and life support requirements performed in the frame of the HUMEX study, the following major critical items have been identified: (i) radiation health risks, mainly occurring during the interplanetary transfer phases and severely augmented in case of an eruption of a solar particle event; (ii) health risks caused by extended periods in microgravity with an unacceptable risk of bone fracture as a consequence of bone demineralisation; (iii) psychological risks as a consequence of long-term isolation and confinement in an environment so far not experienced by humans; (iv) the requirement of bioregenerative life support systems complementary to physico-chemical systems, and of in situ resource utilisation to reach a closure of the life support system to the highest degree possible. Considering these constraints, it has been concluded that substantial research and development activities are required in order to provide the basic information for appropriate integrated risk managements, including efficient countermeasures and tailored life support. Methodological approaches should include research on the ISS, on robotic precursors missions to Mars, in ground-based simulation facilities as well as in analogue natural environments on Earth.

Previous studies have shown that isolated beta-(1,3 and 1,6)-D-glucans and related alkali-extracted fractions from the cell wall of Saccharomyces cerevisiae are able to complex with zearalenone in vitro (affinity up to 50%) and thus may reduce the bioavailability of toxins in the digestive tract. The complexation mechanisms involve cooperative interaction between the two chemical entities that can be computed by Hill's model. Various linear or branched soluble or insoluble beta-D-glucans were evaluated to elucidate their roles in the adsorption mechanisms under three pH conditions (3.0, 6.0, and 8.0) found in the digestive tract. A constant quantity of each beta-D-glucans (1 mg/ml) was mixed at 39 degrees C with increasing amounts of zearalenone (2 to 100 microg/ml), and the amount of bound toxin was measured. Acidic and neutral conditions gave the highest affinity rates (64 to 77%) by beta-(1,3)-D-glucans, whereas alkaline conditions decreased adsorption except when beta-(1,6)-D-glucan side chains were branched on beta-(1,3)-D-glucans. Alkaline conditions appear to impede the active three dimensional conformation of beta-D-glucans and favor single helix and/or random coil structures. Study of the equilibrium between beta-D-glucan-bound and free toxins revealed that two types of chemical interactions occur during toxin complexation with beta-D-glucans, identified as weak chemical linkages such as hydrogen and van der Waals bonds.

Cell walls of yeasts and bacteria are able to complex with mycotoxins and limit their bioavailability in the digestive tract when these yeasts and bacteria are given as feed additives to animals. To identify the component(s) of the yeast cell wall and the chemical interaction(s) involved in complex formation with zearalenone, four strains of Saccharomyces cerevisiae differing in their cell wall glucan and mannan content were tested. Laboratory strains wt292, fks1, and mnn9 were compared with industrial S. cerevisiae strain sc1026. The complex-forming capacity of the yeast cell walls was determined in vitro by modelling the plots of amount of toxin bound versus amount of toxin added using Hill's model. A cooperative relationship between toxin and adsorbent was shown, and a correlation between the amount of beta-D-glucans in cell walls and complex-forming efficacy was revealed (R2 = 0.889). Cell walls of strains wt292 and mnn9, which have higher levels of beta-D-glucans, were able to complex larger amounts of zearalenone, with higher association constants and higher affinity rates than those of the fks1 and sc1026 strains. The high chitin content in strains mnn9 and fks1 increased the alkali insolubility of beta-D-glucans from isolated cell walls and decreased the flexibility of these cell walls, which restricted access of zearalenone to the chemical sites of the beta-D-glucans involved in complex formation. The strains with high chitin content thus had a lower complex-forming capacity than expected based on their beta-D-glucans content. Cooperativity and the three-dimensional structure of beta-D-glucans indicate that weak noncovalent bonds are involved in the complex-forming mechanisms associated with zearalenone. The chemical interactions between beta-D-glucans and zearalenone are therefore more of an adsorption type than a binding type.

The European Space Agency has recently initiated a study of the human responses, limits and needs with regard to the stress environments of interplanetary and planetary missions. Emphasis has been laid on human health and performance care as well as advanced life support developments including bioregenerative life support systems and environmental monitoring. The overall study goals were as follows: (i) to define reference scenarios for a European participation in human exploration and to estimate their influence on the life sciences and life support requirements; (ii) for selected mission scenarios, to critically assess the limiting factors for human health, wellbeing, and performance and to recommend relevant countermeasures; (iii) for selected mission scenarios, to critically assess the potential of advanced life support developments and to propose a European strategy including terrestrial applications; (iv) to critically assess the feasibility of existing facilities and technologies on ground and in space as testbeds in preparation for human exploratory missions and to develop a test plan for ground and space campaigns; (v) to develop a roadmap for a future European strategy towards human exploratory missions, including preparatory activities and terrestrial applications and benefits. This paper covers the part of the HUMEX study dealing with lunar missions. A lunar base at the south pole where long-time sunlight and potential water ice deposits could be assumed was selected as the Moon reference scenario. The impact on human health, performance and well being has been investigated from the view point of the effects of microgravity (during space travel), reduced gravity (on the Moon) and abrupt gravity changes (during launch and landing), of the effects of cosmic radiation including solar particle events, of psychological issues as well as general health care. Countermeasures as well as necessary research using ground-based test beds and/or the International Space Station have been defined. Likewise advanced life support systems with a high degree of autonomy and regenerative capacity and synergy effects were considered where bioregenerative life support systems and biodiagnostic systems become essential. Finally, a European strategy leading to a potential European participation in future human exploratory missions has been recommended.

Three models based on sigmoidal plotting were tested for their ability to describe zearalenone adsorption on Saccharomyces cerevisiae cell walls in vitro. All three models closely fitted the experimental data, but Hill's equation gave the most accurate parameters, and provided information on the physical and chemical mechanisms involved in the adsorption of mycotoxin on yeast cell walls.

International audience; Background: On-site cellulase production using locally available lignocellulosic biomass (LCB) is essential for cost-effective production of 2nd-generation biofuels. Cellulolytic enzymes (cellulases and hemicellulases) must be produced in fed-batch mode in order to obtain high productivity and yield. To date, the impact of the sugar composition of LCB hydrolysates on cellulolytic enzyme secretion has not been thoroughly investigated in industrial conditions. Results: The effect of sugar mixtures (glucose, xylose, inducer) on the secretion of cellulolytic enzymes by a glucose-derepressed and cellulase-hyperproducing mutant strain of Trichoderma reesei (strain CL847) was studied using a small-scale protocol representative of the industrial conditions. Since production of cellulolytic enzymes is inducible by either lactose or cellobiose, two parallel mixture designs were performed separately. No significant difference between inducers was observed on cellulase secretion performance, probably because a common induction mechanism occurred under carbon flux limitation. The characteristics of the enzymatic cocktails did not correlate with productivity, but instead were rather dependent on the substrate composition. Increasing xylose content in the feed had the strongest impact. It decreased by 2-fold cellulase, endoglucanase, and cellobiohydrolase activities and by 4-fold β-glucosidase activity. In contrast, xylanase activity was increased 6-fold. Accordingly, simultaneous high β-glucosidase and xylanase activities in the enzymatic cocktails seemed to be incompatible. The variations in enzymatic activity were modelled and validated with four fed-batch cultures performed in bioreactors. The overall enzyme production was maintained at its highest level when substituting up to 75% of the inducer with non-inducing sugars. Conclusions: The sugar substrate composition strongly influenced the composition of the cellulolytic cocktail secreted by T. reesei in fed-batch mode. Modelling can be used to predict cellulolytic activity based on the sugar composition of the culture-feeding solution, or to fine tune the substrate composition in order to produce a desired enzymatic cocktail.

Background During bioprocess development, secondary screening is a key step at the boundary between laboratory and industrial conditions. To ensure an effective high-throughput screening, miniaturized laboratory conditions must mimic industrial conditions, especially for oxygen transfer, feeding capacity and pH stabilization. Results A feeding strategy has been applied to develop a simple screening procedure, in which a stoichiometric study is combined with a standard miniaturization procedure. Actually, the knowledge of all nutriments and base or acid requirements leads to a great simplification of pH stabilization issue of miniaturized fed-batch cultures. Applied to cellulase production by Trichoderma reesei, this strategy resulted in a stoichiometric mixed feed of carbon and nitrogen sources. While keeping the pH between shake flask and stirred bioreactor comparable, the developed shake flask protocol reproduced the strain behaviour under stirred bioreactor conditions. Compared to a an already existing miniaturized shake flasks protocol, the cellulase concentration was increased 5-fold, reaching about 10 g L-1. Applied to the secondary screening of several clones, the newly developed protocol succeeded in selecting a clone with a high industrial potential. Conclusions The understanding of a bioprocess stoichiometry contributed to define a simpler and more effective miniaturization. The suggested strategy can potentially be applied to other fed-batch processes, for the screening of either strain collections or experimental conditions.

MELiSSA is a microorganism based artificial ecosystem conceived as a tool for understanding the behavior of ecosystems and developing the technology for future Manned Space Missions. MELiSSA is composed of four compartments colonized by the microorganisms required by the function of this ecosystem : breakdown of waste produced by men, regeneration of atmosphere and biosynthesis of edible biomass. This paper reports the mass balance description of a Biological Life Support System composed of the MELiSSA loop and of a Higher Plant Compartment working in parallel with the photosynthetic Spirulina compartment producing edible biomass. The recycling efficiencies of the system are determined and compared for various working conditions of the MELiSSA loop with or without the HPC.

International audience; Three models based on sigmoidal plotting were tested for their ability to describe zearalenone adsorption on Saccharomyces cerevisiae cell walls in vitro. All three models closely fitted the experimental data, but Hill's equation gave the most accurate parameters, and provided information on the physical and chemical mechanisms involved in the adsorption of mycotoxin on yeast cell walls.

MELISSA is a micro-organisms based ecosystem conceived as a tool for understanding the behaviour of artificial ecosystems, and developing the technology for a future biological life support system for long term space mission. The driving element of MELISSA is the recovering of oxygen and edible biomass from waste (faeces, urea). Due to its intrinsic instability and the safety requirements of manned missions, an important control strategy is developed to pilot this system and to optimize its recycling performance. This is a hierarchical control strategy. Each MELISSA compartment has its local control system, and taking into account the states of other compartments and a global desired functioning point, the upper level determines the setpoints for each compartment. The developed approach is based on first principles models of each compartment (physico chemical equations, stoichiometries, kinetic rates, ...). Those models are used to develop a global simulator of the system (in order to study the global functioning). They are also used in the control strategy, which is a non linear predictive model based strategy. This paper presents the general approach of the control strategy of the loop from the compartment level up to the overall loop. At the end, some simulation and experimental results are presented.