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Strain MDTJ8T is a chain-elongating thermophilic bacterium isolated from a thermophilic acidogenic anaerobic digestor treating human waste while producing the high commodity chemical n-caproate. The strain grows and produces formate, acetate, n-butyrate, n-caproate and lactate from mono-, di- and polymeric saccharides at 37–60 °C (optimum, 50–55 °C) and at pH 5.0–7.0 (optimum, pH 6.5). The organism is an obligate anaerobe, is motile and its cells form rods (0.3–0.5×1.0–3.0 µm) that stain Gram-positive and occur primarily as chains. Phylogenetic analysis of both the 16S rRNA gene and full genome sequence shows that strain MDTJ8T belongs to a group that consists of mesophylic chain-elongating bacteria within the family Oscillospiraceae , being nearest to Caproicibacter fermentans EA1T (94.8 %) and Caproiciproducens galactitolivorans BS-1T (93.7 %). Its genome (1.96 Mbp) with a G+C content of 49.6 mol% is remarkably smaller than those of other chain-elongating bacteria of the family Oscillospiraceae . Pairwise average nucleotide identity and DNA–DNA hybridization values between strain MDJT8T and its mesophilic family members are less than 70 and 35 %, respectively, while pairwise average amino acid identity values are less than 68 %. In addition, strain MDJT8T uses far less carbohydrate and non-carbohydrate substrates compared to its nearest family members. The predominant cellular fatty acids of strain MDTJ8T are C14 : 0, C14 : 0 DMA (dimethyl acetal) and C16 : 0, while its polar lipid profile shows three unidentified glycophospholipids, 11 glycolipids, 13 phospholipids and six unidentified lipids. No respiratory quinones and polyamines are detected. Based on its phylogenetic, genotypic, morphological, physiological, biochemical and chemotaxonomic characteristics, strain MDTJ8T represents a novel species and novel genus of the family Oscillospiraceae and Thermocaproicibacter melissae gen. nov., sp. nov. is proposed as its name. The type strain is MDTJ8T (=DSM 114174T=LMG 32615T=NCCB 100883T).

A thermophilic chain elongating bacterium, strain MDTJ8, was isolated from a thermophilic acidogenic anaerobic digestor producing n-caproate from human waste, growing optimally at 50-55 °C and pH 6.5. 16S rRNA gene analysis suggests that MDTJ8 represents a new species/genus within a group currently composed of mesophilic chain elongators of the Oscillospiraceae family. Genome analysis showed that strain MDTJ8 contains homologues of genes encoding for chain elongation and energy conservation but also indicated n-caproate production from carbohydrates including polymeric substances. This was confirmed by culturing experiments in which MDTJ8 converted, at pH 6.5 and 55 °C, mono-, di- and polymeric carbohydrates (starch and hemicellulose) to n-caproate reaching concentrations up to 283 mg/L and accounting for up to 10 % of the measured fermentation products. MDTJ8 is the first axenic organism that thermophilically performs chain elongation, opening doors to understand and intensify thermophilic bioprocesses targeting anaerobic digestion towards the production of the value-added chemical n-caproate.

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.

The ability of cyanobacterium Arthrospira sp. to assimilate waste nitrogen sources (ammonium and urea) makes it an important candidate for wastewater management. The aim of this work was to evaluate a cultivation approach based on continuous-transitional-feeding regime (nitrate-ammonium-nitrate) in a photobioreactor to assess the effects of ammonium salts on Arthrospira sp. PCC 8005 metabolism. Using a comprehensive biochemical, proteomic and stoichiometric profiling of biomass, this study demonstrated that the proposed cultivation approach could increase the proteins and pigments yields by 20-30%, compared to the respective yields obtained from wild-type Arthrospira sp. strain A light-energy-transfer model was used to predict the biomass and oxygen productivities of Arthrospira sp. cultivated under transitional-feeding regime. 95 ± 2% match was observed between the experimental and simulated productivities. This study thus opened new avenues for use of ammonium rich wastewater for commercial production of high value pigments, biofuel and bioplastics using Arthrospira sp.

The aim of this study was to investigate ammonia load removable by a fixed-bed bioreactor. In this study, high ammonia loads, up to 4.5 kgN/m3 d were applied on a fixed bed reactor colonised by two pures nitrifying bacteria: Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25391. The loads were similar to the highest values reported in literature especially with a two bacteria population. The complete ammonia removal efficiency in our installation has reached 2.5 kgN/m3.d for a full nitrification. An N-tank in series model was used to represent the fixed bed reactor and to predict the nitrification in the installation. The developed model was accurate and representative of the nitrification assumed by Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25391. This model was also used to predict the biomass and oxygen concentrations during the experiment under various operational conditions. The biofilm fixed on the solid support (polysterene beads 2 mm diameter) was mainly present in the bottom of the reactor where the ammonia load was applied. It is demonstrated that in this region of the column the oxygen concentrations reached the lowest values.

The MELiSSA (MicroEcological Life Support System Alternative) project is developing a closed regenerative life support system for long-term space missions by considering the integration of six biological compartments tested in a dedicated pilot plant. The technological effort of building such a closed and sustainable ecological system can also have relevant applications for intensive circular resources reutilization at terrestrial level. In this work, the continuous operation and gas phase connection of two elements of the loop (83 L air-lift Limnospira indica photobioreactor (PBR) and a rat isolator (mock crew)) is performed and modelled. The model includes PBR hydrodynamic characterization, gas-liquid mass transfer and cyanobacteria growth, crew consumption and a control system adjusting light intensity according to oxygen demand. The model is validated in a series of tests where crew compartment oxygen setpoints are sequentially changed to test the global dynamics. The obtained results show a good model performance, as indicated in the low relative error (≤ 0.06) and the high Pearson correlation coefficient and Willmott-d-index obtained for the main variable of the system (0.98–1.00), oxygen concentration, in all cases.

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...

The production of alcoholic beverages is based on the production of alcohol and aroma by fermentation, in most cases by the yeast Saccharomyces cerevisiae. The overall objective of this chapter is to improve our understanding of the genetic and environmental factors that control the production of the metabolites (ethanol, higher alcohols, and esters) involved in alcoholic beverages. This chapter aims at developing a comprehensive framework for establishing models of yeast growth and the production of metabolites. A general survey of some of the latest studies on yeast metabolism is presented with the aim of getting a better understanding of the production of the main compounds produced during the winemaking and brewery processes.

The aim of the present work was to study the growth of two nitrifying bacteria. For modelling the nitrifying subsystem of the MELiSSA loop, Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25931 were grown separately and in cocultures. The kinetic parameters of a stoichiometric mass balanced Pirt model were identified: μ max = 0.054 h −1 , decay rate b = 0.003 h −1 and maintenance rate m = 0.135 gN-NH 4 + ·gX −1 ·h −1 for Nitrosomonas europaea ; μ max = 0.024 h −1 , b = 0.001 h −1 and m = 0.467 gN-NO 2 − ·gX −1 ·h −1 for Nitrobacter winogradskyi . A predictive structured model of nitrification in co-culture was developed. The online evolution of the addition of KOH is correlated to the nitritation; the dissolved oxygen concentration is correlated to both nitritation and nitratation. The model suitably represents these two variables so that transient partial nitrification is assessed. This is a clue for avoiding partial nitrification by predictive functional control.

This study focuses on the use of acetic acid as carbon source for cell mass and lipid production using an oleaginous yeast, Cryptococcus curvatus. To improve this cell mass and lipid production on acetic acid, a numerical model was built to predict the yeast behavior. The model was first calibrated and validated on a fed-batch culture of the oleaginous yeast grown on acetic acid. After the validation step, this model was used as a predictive tool to search for optimal dilution rate and C/N ratios for continuous culture. A continuous culture was then launched using these culture parameters, revealing that the experimental data fitted the model predictions. At steady-state, cell mass concentration was stabilized at 26.7 g/L containing 48–53% of lipid content. A maximal lipid productivity of 0.54 g L−1 h−1 was obtained, which was superior to those reported in literature. This model could be qualified as a mechanistic one since it allows understanding reactions underlying the lipid production process. The experimental data fitted the model predictions, which confirmed that the use of a model is a powerful and predictive tool which could help the operator to process parameters to improve the culture.

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.

The improvement of culture parameters for lipid production from acetate as carbon source was investigated using the oleaginous yeast Cryptococcus curvatus. A new pH regulation system dispensing acetate was developed for fed-batch culture and allowed obtaining nearly 80 g/L biomass within 60 h with a maximal growth rate of 0.28 h(-1). A biological model was developed from experimental data. The influence of three C/N ratios of 300, 500 and 900 were tested during a multi-phases process on lipid accumulation. The C/N ratio of 300 was reported to be the most suitable for lipid storage. No significant increase of lipids content was obtained with higher value. A maximal content of 60% DCW of lipid was obtained. The determination of fatty acids profiles of the microbial oils has confirmed that the valorization of acetate by microbial oils production was a promising perspective.

International audience; Cereus triangularis (Cactaceae) is a cactus used in food decoction as a traditional medicine in the North region of Madagascar to reduce stomach ache and intestinal diseases. Hydrocolloids were sequentially extracted from its cladodes with a yield of 24% (240 mg/g based on dried cladodes powder). Structural analyses has revealed that this polysaccharide with a molecular mass of 8430,000 g/mol was mainly composed of a galactan backbone of a (1 → 4) linked β-d-Galp residues probably substituted at position 3 by l-arabinofuranosyl residues. In vitro antioxidant activity of this arabinogalactan-rich fraction was detected and quantified by radical DPPH scavenging, hydroxyl radical scavenging, radical anion superoxide scavenging and reducing power method.

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.

The operation of a fixed bed biofilm reactor for nitrification colonized by Nitrosomonas europaea and Nitrobacter winogradskyi has been characterized in terms of steady state operation but also studying the dynamics of the system in front of disturbances of ammonium load. The nitrifying reactor is used in a biological life support system (BLSS) in which it is necessary to assure high conversion to nitrate and to avoid nitrite production. In order to enhance the knowledge on the system and also as a simulation and control tool, a mathematical model has been developed, calibrated and validated for both steady state and dynamic conditions of continuous mode operation. The results presented demonstrate the applicability of the model to the experimental system, providing a simple and useful mathematical tool to be further applied to the control of the reactor and to maintain the long-term stability of a loop of interconnected bioreactors in the BLSS.

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.

International audience; The isolated cell wall of Saccharomyces cerevisiae has some capacity to adsorb zearalenone (affinity near 30%) and reduce the bioavailability of toxins in the digestive tract. The adsorption process was quantified in vitro, and the data obtained when plotted with Hill's equation indicated a cooperative process. The model showed that the adsorption capacity was related to the yeast cell wall composition. This work focused on the role of various beta-D-glucan types in the efficacy of zearalenone adsorption by yeast cell wall and sought to elucidate some of the adsorption mechanisms. Zearalenone was mixed at 37 degreesC with a constant quantity of alkali-soluble or alkali-insoluble beta-D-glucans isolated from yeast cell walls, and the amount of adsorbed zearalenone was measured. Given that the alkali solubility of beta-D-glucans is a determining factor for their three-dimensional conformation and that the alkali-insoluble fraction had a greater affinity (up to 50%) than the alkali-soluble fraction (similar to16%), it was concluded that the three-dimensional structure strongly influences the adsorption process. The alkali insolubility of beta-D-glucans led to the formation of single and/or triple helices, which have been identified as the most favorable structures for zearalenone adsorption efficacy. The beta(1,3)-D-glucan and beta(1,6)-D-glucan compositions of the two alkali-extracted fractions and their involvement in the adsorption process are discussed.

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.

The behavior of pure cultures of nitrifying microorganisms under autotrophic growth operating conditions was investigated and the relations between their energy metabolism and their anabolism analyzed by means of metabolic network computation. The description of the metabolism of the nitrifiers is extended to their energy metabolism by introducing compartmentalization (cytoplasmic and periplasmic sides) and studying coupling between the electron transport chain and the proton gradient generation. The energy model of Nitrosomonas and Nitrobacter was developed based on the oxidoreduction reactions known to be involved. The electron transport chains and the associated proton translocation for these models are described. Several possible hypotheses are analyzed and discussed concerning the thermodynamic consistency of all the oxidoreduction reactions. For Nitrosomonas, the most delicate point is the second step of hydroxylamine oxidation. For Nitrobacter a new energy model is proposed in which NO plays an important role as node in the distribution of electrons from NO(2)(-) oxidation to the membrane electron transport chain. The compartmentalization enables us to consider a proton gradient dissipation flux as the expression of the overall energy loss in metabolic analysis (the so-called maintenance phenomena). The energy model (electron transport chain, proton gradient) is associated with an overall description of the metabolism of Nitrosomonas and Nitrobacter in terms of metabolic flux calculation. This representation demonstrates that a maintenance in nitrifiers expressed as a proton leak is no higher than for other aerobes. The yields calculated from the energy models integrated with the metabolic models of nitrifiers are consistent with the experimental yields in the literature.

A dynamic model for a fixed bed nitrifying column with recirculation of the liquid and gas phases was developed. Liquid RTD experiments demonstrated that the liquid phase was perfectly mixed inside the column. Hete- rogeneity of biomass distribution on the solid phase (beads) was represented by an N-tanks in series model, and a back-mixing term was set to account for the well-mixed liquid phase throughout the column. In autotrophic conditions, competition for oxygen is the cause of the spatial segregation of the two species. Nitrosomonas is concentrated on beads at the bottom of the bed whereas Nitrobacter is more widely distributed. This is consistent with biomass distribution results reported by Cox et al. [17] in a nitrifying fixed bed column. Nitrification takes place at the bottom of the column, always in oxygen gas-liquid mass transfer limiting conditions. Nevertheless, considering the whole process, nitrification is complete (>98% of NH3 oxidised) and there is no oxygen limitation (the outlet dissolved oxygen concentration is not limiting). The dynamic behaviour of the column, in conditions set up to avoid biofilm diffusion limitation, was simulated for different NH3-load variations and oxygen shutdowns. The simulated behaviour of the column can be compared to results reported by Bazin et al. [16]. This confirms that the output transient nitrite peaks are higher when changes in the process conditions produce a rearrangement of biomass distribution in the fixed bed.

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.

The artificial ecosystem MELiSSA, supported by the European Space Agency is a closed loop system consisting of 5 compartments in which food, water and oxygen are produced out of organic waste. The first compartment is conceived as a thermophilic anaerobic membrane bioreactor liquefying organic waste into VFAs, ammonium and CO 2 without methane. A 20 L reactor was assembled to demonstrate the selected design and process at prototype scale. We characterized system performance from start-up to steady state and evaluated process efficiencies with special attention drawn to the mass balances. An overall efficiency for organic matter biodegradation of 50% was achieved. The dry matter content was stabilized around 40–50 g L −1 and VFA production around 5–6 g L −1 . The results were consistent for the considered substrate mixture and can also be considered relevant in a broader context, as a first processing step to produce building blocks for synthesis of primary energy vectors.

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.

As a part of a natural biological N-cycle, nitrification is one of the steps included in the conception of artificial ecosystems designed for extraterrestrial life support systems (LSS) such as Micro-Ecological Life Support System Alternative (MELiSSA) project, which is the LSS project of the European Space Agency. Nitrification in aerobic environments is carried out by two groups of bacteria in a two-step process. The ammonia-oxidizing bacteria (Nitrosomonas europaea) realize the oxidation of ammonia to nitrite, and the nitrite-oxidizing bacteria (Nitrobacter winogradskyi), the oxidation of nitrite to nitrate. In both cases, the bacteria achieve these oxidations to obtain an energy and reductant source for their growth and maintenance. Furthermore, both groups also use CO2 predominantly as their carbon source. They are typically found together in ecosystems, and consequently, nitrite accumulation is rare. Due to the necessity of modeling accurately conversion yields and transformation rates to achieve a complete modeling of MELiSSA, the present study focuses on the experimental determination of nitrogen to biomass conversion yields. Kinetic and mass balance studies for axenic cultures of Nitrosomonas europaea and Nitrobacter winogradskyi in autotrophic conditions are performed. The follow-up of these cultures is done using flow cytometry for assessing biomass concentrations and ionic chromatography for ammonium, nitrite, and nitrate concentrations. A linear correlation is observed between cell count and optical density (OD) measurement (within a 10 % accuracy) validating OD measurements for an on-line estimation of biomass quantity even at very low biomass concentrations. The conversion between cell count and biomass concentration has been determined: 7.1 × 1012 cells g dry matter (DM)−1 for Nitrobacter and 6.3 × 1012 cells g DM−1 for Nitrosomonas. Nitrogen substrates and products are assessed redundantly showing excellent agreement for mass balance purposes and conversion yields determination. Although the dominant phenomena are the oxidation of NH 4 + into nitrite (0.95 mol mol N−1 for Nitrosomonas europaea within an accuracy of 3 %) and nitrite into nitrate (0.975 mol mol N−1 for Nitrobacter winogradskyi within an accuracy of 2 %), the Nitrosomonas europaea conversion yield is estimated to be 0.42 g DM mol N−1, and Nitrobacter winogradskyi conversion yield is estimated to be 0.27 g DM mol N−1. The growth rates of both strains appear to be dominated by the oxygen transfer into the experimental setups.

Manmade ecosystems differ from their prototype biosphere by the principle of control. The Earth Biosphere is sustainable by stochastic control and very large time constants. By contrast, in a closed ecosystem such as the micro-ecological life support system alternative (MELiSSA system) developed by the European Space Agency for space exploration, a deterministic control is a prerequisite of sustainable existence. MELiSSA is an integrated sum of interconnected biological subsystems. On one hand, all unit operations in charge of the elementary functions constitutive of the entire life support system are studied until a thorough understanding and mathematical modelling. On the other hand, the systemic approach of complex, highly branched systems with feedback loops is performed. This leads to study in the same perspective, with the same degree of accuracy and with the same language, waste degradation, water recycling, atmosphere revitalisation and food production systems prior to the integration of knowledge-based control models. This paper presents the mathematical modelling of the MELiSSA system and the interface between the control strategy of the entire system and the control of the bioreactors.

In a previous paper we reported that beta-D-glucans isolated from Saccharomyces cerevisiae could adsorb zearalenone, reduce its bioavailability in the digestive tract, and protect animals against its adverse effects. We have now investigated, in vitro, the kinetics of the interaction between other mycotoxins and beta-D-glucans from several sources at three pH values found along the digestive tract (3.0, 6.0, and 8.0). Acid and neutral conditions gave the highest affinity rates for aflatoxins B1 > deoxynivalenol > ochratoxin A and involved both the (1 --> 3)-beta-D-glucans and the (1 --> 6)-beta-D-glucans. Alkaline conditions, owing to their destructuring action on glucans, were favorable only for the adsorption of patulin. Using molecular mechanics, we found that hydroxyl, ketone, and lactone groups are involved in the formation of both hydrogen bonds and van der Waals interactions between aflatoxins B1, deoxynivalenol and patulin, and beta-D-glucans. Differences in the binding capacity of the mycotoxins are due to their specific physical and chemical characteristics.

This paper introduces two modeling approaches in consideration for the MELiSSA Higher Plants Compartment. This includes an empirical light response curve modeling approach and the Modified Energy Cascade (MEC) model. The MEC model was translated into EcosimPro and evaluated for its performance under a range of environment conditions. The model demonstrated an adequate response to changes on the environmental conditions (temperature, CO 2 concentration and light flux) predicting the gas exchange (O 2 production, CO 2 consumptions, and water vapor transpiration).

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.

The determination of k(L) a by a gas balance method coupled with sulphite oxidation is compared for three kinds of processes (stirred tank, bubble column and fixed-bed column reactors) with a gassing-in and with a classical chemical sulphite oxidation method. The mathematical relations required for the determination of the k(L) a value are detailed. In coalescing gas-liquid conditions, the values calculated by the three methods are shown to be comparable. The gas balance method is more rapid than either the steady-state gassing-in or the chemical sulphite reaction rate measurement methods. It is also well adapted for three-phase systems (gas-liquid-solid) in which the non-coalescing effects of sulphite solution are reduced by solid interferences.

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.