Hydrogen production by the hyperthermophilic bacterium Thermotoga maritima part I: effects of sulfured nutriments, with thiosulfate as model, on hydrogen production and growth

International audienceBackground: Thermotoga maritima and T. neapolitana are hyperthermophile bacteria chosen by many research teams to produce bio-hydrogen because of their potential to ferment a wide variety of sugars with the highest theoretical H-2/glucose yields. However, to develop economically sustainable bio-processes, the culture medium formulation remained to be optimized. The main aim of this study was to quantify accurately and specifically the effect of thiosulfate, used as sulfured nutriment model, on T. maritima growth, yields and productivities of hydrogen. The results were obtained from batch cultures, performed into a bioreactor, carefully controlled, and specifically designed to prevent the back-inhibition by hydrogen. Results: Among sulfured nutriments tested, thiosulfate, cysteine, and sulfide were found to be the most efficient to stimulate T. maritima growth and hydrogen production. In particular, under our experimental conditions (glucose 60 mmol L-1 and yeast extract 1 g L-1), the cellular growth was limited by thiosulfate concentrations lower than 0.06 mmol L-1. Under these conditions, the cellular yield on thiosulfate (Y X/Thio) could be determined at 3617 mg mmol(-1). In addition, it has been shown that the limitations of T. maritima growth by thiosulfate lead to metabolic stress marked by a significant metabolic shift of glucose towards the production of extracellular polysaccharides (EPS). Finally, it has been estimated that the presence of thiosulfate in the T. maritima culture medium significantly increased the cellular and hydrogen productivities by a factor 6 without detectable sulfide production. Conclusions: The stimulant effects of thiosulfate at very low concentrations on T. maritima growth have forced us to reconsider its role in this species and more probably also in all thiosulfato-reducer hyperthermophiles. Henceforth, thiosulfate should be considered in T. maritima as (1) an essential sulfur source for cellular materials when it is present at low concentrations (about 0.3 mmol g(-1) of cells), and (2) as both sulfur source and detoxifying agent for H-2 when thiosulfate is present at higher concentrations and, when, simultaneously, the pH(2) is high. Finally, to improve the hydrogen production in bio-processes using Thermotoga species, it should be recommended to incorporate thiosulfate in the culture medium

Multi-objective Optimization of Thermophilic Biohydrogen Production

Dynamic optimization of thermophilic hydrogen and by-product production requires the use of robust models coupled with control strategies. In this work, a model was used to optimize biohydrogen (bioH2) and acetate production using Thermotoga maritima (T. maritima) with a Multi-Objective Optimization (MOO). The aim was to find the trade-off between the maxima of yield and productivity of the hydrogen production and acetate in a continuous dark fermentation process by modifying the inlet liquid flow rate. A dynamic mass balance model was used to optimize thermophilic bioH2 and acetate production using T. maritima MSB8 (DSMZ 3109) strains.

Etude de la biodiversité bactérienne d'un biotope oléicole hypersalé et des voies biochimiques impliquées dans la transformation du tyrosol

Les effluents liquides qui sont composés d'un mélange de margines et d'eaux de saumures, sont rejetés par les industries oléicoles, et contribuent considérablement à la pollution environnementale du pourtour méditerranéen. Ils sont caractérisés par une forte DCO et des quantités significatives de composés phénoliques peu biodégradables, dont le plus représentatif est le tyrosol. L objectif de ce travail était donc de comprendre les voies dégradatrices du tyrosol, via l'utilisation de microorganismes endogènes isolés de ces effluents. En utilisant la technique 'Single Strand Conformation Polymorphism' (SSCP), l'étude de la biodiversité a montré un profil de biotope hypersalé. Différents isolats bactériens halophiles, aérobies et anaérobies ont alors été obtenus grâce à un isolement classique ciblé. Deux d'entre eux, TYRC17 et HTB24, appartenant au genre Halomonas, ont été retenus pour leur capacité à transformer le tyrosol et le p-hydroxyphénylacétate (HPA), en molécules ortho-diphénoliques (3,4-dihydroxyphénylacétate ou DHPA et homogentisate ou HGA), connues comme des antioxydants potentiels. Cette étude nous a permis de mettre en évidence le métabolisme de dégradation du tyrosol, encore jamais décrit à ce jour. Ainsi, le tyrosol est oxydé via une aryle-déshydrogénase en HPA. Ce dernier est à son tour hydroxylé soit en HGA via une HPA 1-monooxygénase chez la souche TYRC17, soit en DHPA via une HPA 3- monooxygénase chez la souche HTB24. Ces composés ortho-diphénoliques sont alors clivés par des catécholdioxygénases, et enfin dégradés. En présence de métaux de transition comme ceux contenus dans les oligoéléments ajoutés, l HGA se transforme abiotiquement en 2,5-dihydroxybenzaldehyde (gentisaldehyde), qui intervient dans la formation de la pyomélanine. Quant à la souche HTB24, elle produit de l hydroxytyrosol par hydroxylation aspécifique du tyrosol, via l HPA 3-monooxygénase qui a été induite par le HPA. De plus, l analyse d'autres bactéries possédant cette enzyme, telles que P. aeruginosa ou E. coli, a confirmé qu elles étaient aussi capables de transformer le tyrosol en hydroxytyrosol. Ces bioconversions originales ouvrent donc de fortes perspectives pour la bioremédiation de ces effluents fortement salés, mais aussi pour une production prometteuse de molécules antioxydantes à haute valeur ajoutéeThe liquid effluents which are composed of a mixture of olive mill wastewater and brine waters, are rejected by olive industries, and contribute considerably to the environmental pollution of the Mediterranean area. They are characterized by a high DCO and significant quantities of recalcitrant phenolic compounds, of which the most representative is the tyrosol. The objective of this work was thus to understand the degradation pathways of the tyrosol, via the use of endogenous microorganisms isolated from these effluents. By using the technique ' Single Strand Conformation Polymorphism' (SSCP), the study of the biodiversity showed a profile of salted biotope. Various halophilous, aerobic and anaerobic bacterial isolates were then obtained through a targeted traditional insolation. Two of them, TYRC17 an HTB24, belonging to the Halomonas genus, were studied for their capacity to transform the tyrosol and p - hydroxyphenylacetate d (HPA), into orthodiphenolic molecules (3,4-dihydroxyphenylacetate or DHPA and homogentisate HGA), known as potential antioxydants. This study enabled us to highlight two degradation pathways of the tyrosol, never yet described to date. Thus, the tyrosol is oxidized via an aryl-dehydrogenase in HPA. This last is hydroxylated either in HGA via a HPA 1-monooxygenase from strain TYRC17, or in DHPA via a HPA 3-monooxygenase from strain HTB24. These ortho-diphenolic compounds are then cleaved by catechol-dioxygenases, and finally degraded. In the presence of transition metals, contained in the Widdel oligo-element solution, the HGA is transformed not biologically, into 2,5-dihydroxybenzaldehyde (gentisaldehyde) which is involved in the pyomelanin formation. Moreover, strain HTB24 is able to produce hydroxytyrosol by aspecific tyrosol hydroxylation, via the same HPA 3-monooxygenase, the latter being induced by the presence of HPA in the medium. Moreover, the study of other bacteria having this enzyme, such as Pseudomonas aeruginosa or Escherichia coli confirmed that they are also able to transform the tyrosol into hydroxytyrosol. These original bioconversions thus open great prospects for the bioremediation for these strongly salted effluents, but also for a promising production of antioxydant molecules with high added valueAIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Engineering Hydrogenases for H2 Production: Bolts and Goals

International audienceHydrogenases are efficient biological catalysts of H2 oxidation and production. Most of them are inhibited by oxygen, and a prerequisite for their use in biotechnological applications under air is to improve their oxygen tolerance. A few bacteria, however, contain hydrogenases that activate H2 even in the presence of O2. Intriguingly, molecular, kinetic and spectroscopic studies lead to assume that different mechanisms might be responsible for the resistance, depending on the enzyme type. In order to better understand the molecular bases of resistance to O2 inhibition, this chapter focuses on the hydrogenases and their reaction with O2 and examines the different strategies to lead to engineer kinetically efficient hydrogenases operating under aerobic conditions

Towards engineering O 2 -tolerance in [Ni–Fe] hydrogenases

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Spark of Life: Role of Electrotrophy in the Emergence of Life

The emergence of life has been a subject of intensive research for decades. Different approaches and different environmental “cradles” have been studied, from space to the deep sea. Since the recent discovery of a natural electrical current through deep-sea hydrothermal vents, a new energy source is considered for the transition from inorganic to organic. This energy source (electron donor) is used by modern microorganisms via a new trophic type, called electrotrophy. In this review, we draw a parallel between this metabolism and a new theory for the emergence of life based on this electrical electron flow. Each step of the creation of life is revised in the new light of this prebiotic electrochemical context, going from the evaluation of similar electrical current during the Hadean, the CO2 electroreduction into a prebiotic primordial soup, the production of proto-membranes, the energetic system inspired of the nitrate reduction, the proton gradient, and the transition to a planktonic proto-cell. Finally, this theory is compared to the two other theories in hydrothermal context to assess its relevance and overcome the limitations of each. Many critical factors that were limiting each theory can be overcome given the effect of electrochemical reactions and the environmental changes produced

Enhancement of fermentative hydrogen production by Thermotoga maritima through hyperthermophilic anaerobic co-digestion of fruit-vegetable and fish wastes

International audienceIn this work, different proportions of model fruit and vegetable wastes (MFVW) and acid hydrolyzed fish wastes (AHFW) were used for hydrogen production in a minimum culture medium based on seawater. Experiments were performed in pH-controlled Stirred Tank Reactor (STR) with or without the addition of nitrogen and sulfur sources. The total H2 production and the maximum hydrogen productivity of T. maritima in the culture medium, containing MFVW and AHFW (45 mmol L−1 carbohydrates) at a C/N ratio of 12, were 132 mmol L−1 and 15 mmol h−1 L−1, respectively. However, tripling the concentration of carbohydrates to reach a C/N ratio of 22, has increased two times the maximum H2 productivity (28 mmol h−1 L−1) due to the improvement in nutrient balance. The cumulative H2 production was 285 mmol L−1, yielding a potential energy generation of 0.12103 MJ ton−1 wastes, which could be an interesting alternative for energy recovery

Hydroxytyrosol from tyrosol using hydroxyphenylacetic acid-induced bacterial cultures and evidence of the role of 4-HPA 3-hydroxylase

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Bioconversion of tyrosol into hydroxytyrosol and 3,4-dihydroxyphenylacetic acid under hypersaline conditions by the new Halomonas sp. strain HTB24

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