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1.
Influence of Hydrogen Electron Donor, Alkaline pH, and High Nitrate Concentrations on Microbial Denitrification: A Review.
Albina, P, Durban, N, Bertron, A, Albrecht, A, Robinet, JC, Erable, B
International journal of molecular sciences. 2019;(20)
Abstract
Bacterial respiration of nitrate is a natural process of nitrate reduction, which has been industrialized to treat anthropic nitrate pollution. This process, also known as "microbial denitrification", is widely documented from the fundamental and engineering points of view for the enhancement of the removal of nitrate in wastewater. For this purpose, experiments are generally conducted with heterotrophic microbial metabolism, neutral pH and moderate nitrate concentrations (<50 mM). The present review focuses on a different approach as it aims to understand the effects of hydrogenotrophy, alkaline pH and high nitrate concentration on microbial denitrification. Hydrogen has a high energy content but its low solubility, 0.74 mM (1 atm, 30 °C), in aqueous medium limits its bioavailability, putting it at a kinetic disadvantage compared to more soluble organic compounds. For most bacteria, the optimal pH varies between 7.5 and 9.5. Outside this range, denitrification is slowed down and nitrite (NO2-) accumulates. Some alkaliphilic bacteria are able to express denitrifying activity at pH levels close to 12 thanks to specific adaptation and resistance mechanisms detailed in this manuscript, and some bacterial populations support nitrate concentrations in the range of several hundred mM to 1 M. A high concentration of nitrate generally leads to an accumulation of nitrite. Nitrite accumulation can inhibit bacterial activity and may be a cause of cell death.
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2.
How to make the reducing power of H2 available for in vivo biosyntheses and biotransformations.
Lauterbach, L, Lenz, O
Current opinion in chemical biology. 2019;:91-96
Abstract
Solar-driven electrolysis enables sustainable production of molecular hydrogen (H2), which represents a cheap and carbon-free reductant. Knallgas bacteria like Ralstonia eutropha are able to split H2 to supply energy in form of ATP and NADH, which can be subsequently used to power reactions of interest. R. eutropha employs the Calvin-Benson-Bassham cycle for the fixation of CO2, which is considered as an abundant and non-competing raw material. In this article, we summarize state-of-the-art approaches for H2-driven biosyntheses using engineered R. eutropha. Furthermore, we describe strategies for synthetic H2-driven NADH recycling. Major challenges for technical application and future perspectives are discussed.
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3.
Biological hydrogen production: molecular and electrolytic perspectives.
Mahidhara, G, Burrow, H, Sasikala, C, Ramana, CV
World journal of microbiology & biotechnology. 2019;(8):116
Abstract
Exploration of renewable energy sources is an imperative task in order to replace fossil fuels and to diminish atmospheric pollution. Hydrogen is considered one of the most promising fuels for the future and implores further investigation to find eco-friendly ways toward viable production. Expansive processes like electrolysis and fossil fuels are currently being used to produce hydrogen. Biological hydrogen production (BHP) displays recyclable and economical traits, and is thus imperative for hydrogen economy. Three basic modes of BHP were investigated, including bio photolysis, photo fermentation and dark fermentation. Photosynthetic microorganisms could readily serve as powerhouses to successively produce this type of energy. Cyanobacteria, blue green algae (bio photolysis) and some purple non-sulfur bacteria (Photo fermentation) utilize solar energy and produce hydrogen during their metabolic processes. Ionic species, including hydrogen (H+) and electrons (e-) are combined into hydrogen gas (H2), with the use of special enzymes called hydrogenases in the case of bio photolysis, and nitrogenases catalyze the formation of hydrogen in the case of photo fermentation. Nevertheless, oxygen sensitivity of these enzymes is a drawback for bio photolysis and photo fermentation, whereas, the amount of hydrogen per unit substrate produced appears insufficient for dark fermentation. This review focuses on innovative advances in the bioprocess research, genetic engineering and bioprocess technologies such as microbial fuel cell technology, in developing bio hydrogen production.
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4.
Advances in research on treatment of heart failure with nitrosyl hydrogen.
Guo, Y, Xu, J, Wu, L, Deng, Y, Wang, J, An, J
Heart failure reviews. 2019;(6):941-948
Abstract
Heart failure is the end stage of various heart diseases such as ischemic heart disease, dilated cardiomyopathy, valvular heart disease, congenital heart disease, and hypertensive myocardial damage. It is characterized by a decrease in myocardial contractility, but there is currently no ideal treatment. Nitroxyl hydrogen (HNO) is considered to be a protonated form of NO. It has special chemical properties compared to other nitrogen oxides. In the body of organisms, HNO can participate in all aspects of the occurrence and development of heart failure (HF) and react with some proteins closely related to cardiac activity, changing its spatial structure and exerting cardioprotective effects. In recent years, studies have shown that HNO can inhibit cardiomyocyte hypertrophy, reduce inflammation, enhance myocardial contractility, dilate coronary arteries as well as peripheral blood vessels in early heart failure, and protect the heart against heart failure. This paper, combined with the latest research results at home and abroad, clarifies that nitrosyl hydrogen exerts cardioprotective effects through various processes that occur in the development of heart failure.
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5.
Catalytic Metallopolymers from [2Fe-2S] Clusters: Artificial Metalloenzymes for Hydrogen Production.
Karayilan, M, Brezinski, WP, Clary, KE, Lichtenberger, DL, Glass, RS, Pyun, J
Angewandte Chemie (International ed. in English). 2019;(23):7537-7550
Abstract
Reviewed herein is the development of novel polymer-supported [2Fe-2S] catalyst systems for electrocatalytic and photocatalytic hydrogen evolution reactions. [FeFe] hydrogenases are the best known naturally occurring metalloenzymes for hydrogen generation, and small-molecule, [2Fe-2S]-containing mimetics of the active site (H-cluster) of these metalloenzymes have been synthesized for years. These small [2Fe-2S] complexes have not yet reached the same capacity as that of enzymes for hydrogen production. Recently, modern polymer chemistry has been utilized to construct an outer coordination sphere around the [2Fe-2S] clusters to provide site isolation, water solubility, and improved catalytic activity. In this review, the various macromolecular motifs and the catalytic properties of these polymer-supported [2Fe-2S] materials are surveyed. The most recent catalysts that incorporate a single [2Fe-2S] complex, termed single-site [2Fe-2S] metallopolymers, exhibit superior activity for H2 production.
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6.
Bioenergetic aspects of archaeal and bacterial hydrogen metabolism.
Pinske, C
Advances in microbial physiology. 2019;:487-514
Abstract
Hydrogenases are metal-containing biocatalysts that reversibly convert protons and electrons to hydrogen gas. This reaction can contribute in different ways to the generation of the proton motive force (PMF) of a cell. One means of PMF generation involves reduction of protons on the inside of the cytoplasmic membrane, releasing H2 gas, which being without charge is freely diffusible across the cytoplasmic membrane, where it can be re-oxidized to release protons. A second route of PMF generation couples transfer of electrons derived from H2 oxidation to quinone reduction and concomitant proton uptake at the membrane-bound heme cofactor. This redox-loop mechanism, as originally formulated by Mitchell, requires a second, catalytically distinct, enzyme complex to re-oxidize quinol and release the protons outside the cell. A third way of generating PMF is also by electron transfer to quinones but on the outside of the membrane while directly drawing protons through the entire membrane. The cofactor-less membrane subunits involved are proposed to operate by a conformational mechanism (redox-linked proton pump). Finally, PMF can be generated through an electron bifurcation mechanism, whereby an exergonic reaction is tightly coupled with an endergonic reaction. In all cases the protons can be channelled back inside through a F1F0-ATPase to convert the 'energy' stored in the PMF into the universal cellular energy currency, ATP. New and exciting discoveries employing these mechanisms have recently been made on the bioenergetics of hydrogenases, which will be discussed here and placed in the context of their contribution to energy conservation.
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7.
Breath Hydrogen Testing in East and Southeast Asia.
Yao, CK, Chu, NHS, Tan, VPY
Journal of clinical gastroenterology. 2018;(3):185-193
Abstract
Breath hydrogen tests are popular, noninvasive tests for the assessment of carbohydrate fermentation in patients with irritable bowel syndrome (IBS) and functional dyspepsia (FD). There is limited information regarding the utility of breath hydrogen and methane tests in IBS and FD patients in East and Southeast Asia. This review aims to summarize current literature about common indications of breath testing in this region, the genesis of functional gastrointestinal symptoms by provocative breath testing and provide suggestions for correct use. The most common testing indication is the assessment of lactose intolerance, followed by small intestinal bacterial overgrowth (SIBO) and differentiation of intestinal gas profiles in research setting. Studies in this region not only documented a high prevalence of lactose malabsorption but a population, both healthy and IBS, that is highly symptomatic to typical lactose intakes. Breath hydrogen assessment of other fermentable carbohydrates (FODMAPs) are fairly uncommon, whereas methane breath testing is almost nonexistent. Cumulative hydrogen production following lactulose was also not excessive in IBS patients compared with controls. The evidence however, for the detection of SIBO suggests limited reliability in the use of lactulose or glucose breath testing alone and inconclusive data on its correlation with symptoms. Conversely, little has been carried out in FD. In conclusion, breath testing should be limited in the predicting patients with SIBO for directing clinical management but can be considered in the objective assessment of lactose malabsorption within a low FODMAP diet. Recommendations to improve the interpretation of breath testing in research were also provided.
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8.
Fixation of carbon dioxide by a hydrogen-oxidizing bacterium for value-added products.
Yu, J
World journal of microbiology & biotechnology. 2018;(7):89
Abstract
With rapid technology progress and cost reduction, clean hydrogen from water electrolysis driven by renewable powers becomes a potential feedstock for CO2 fixation by hydrogen-oxidizing bacteria. Cupriavidus necator (formally Ralstonia eutropha), a representative member of the lithoautotrophic prokaryotes, is a promising producer of polyhydroxyalkanoates and single cell proteins. This paper reviews the fundamental properties of the hydrogen-oxidizing bacterium, the metabolic activities under limitation of individual gases and nutrients, and the value-added products from CO2, including the products with large potential markets. Gas fermentation and bioreactor safety are discussed for achieving high cell density and high productivity of desired products under chemolithotrophic conditions. The review also updates the recent research activities in metabolic engineering of C. necator to produce novel metabolites from CO2.
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9.
Photo-fermentative hydrogen production from crop residue: A mini review.
Zhang, Q, Wang, Y, Zhang, Z, Lee, DJ, Zhou, X, Jing, Y, Ge, X, Jiang, D, Hu, J, He, C
Bioresource technology. 2017;:222-230
Abstract
Photofermentative hydrogen production from crop residues, if feasible, can lead to complete conversion of organic substances to hydrogen (and carbon dioxide). This mini review lists the studies on photofermentative hydrogen production using crop residues as feedstock. Pretreatment methods, substrate structure, mechanism of photosynthetic bacteria growth and metabolism were discussed. Photofermentative hydrogen production from pure culture, consortia and mutants, and the geometry, light sources, mass transfer resistances and the operational strategies of the photo-bioreactor were herein reviewed. Future studies of regulation mechanism of photosynthetic bacteria, such as highly-efficient strain breeding and gene reconstruction, and development of new-generation photo-bioreactor were suggested.
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10.
Enzymes as modular catalysts for redox half-reactions in H2-powered chemical synthesis: from biology to technology.
Reeve, HA, Ash, PA, Park, H, Huang, A, Posidias, M, Tomlinson, C, Lenz, O, Vincent, KA
The Biochemical journal. 2017;(2):215-230
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Abstract
The present study considers the ways in which redox enzyme modules are coupled in living cells for linking reductive and oxidative half-reactions, and then reviews examples in which this concept can be exploited technologically in applications of coupled enzyme pairs. We discuss many examples in which enzymes are interfaced with electronically conductive particles to build up heterogeneous catalytic systems in an approach which could be termed synthetic biochemistry We focus on reactions involving the H+/H2 redox couple catalysed by NiFe hydrogenase moieties in conjunction with other biocatalysed reactions to assemble systems directed towards synthesis of specialised chemicals, chemical building blocks or bio-derived fuel molecules. We review our work in which this approach is applied in designing enzyme-modified particles for H2-driven recycling of the nicotinamide cofactor NADH to provide a clean cofactor source for applications of NADH-dependent enzymes in chemical synthesis, presenting a combination of published and new work on these systems. We also consider related photobiocatalytic approaches for light-driven production of chemicals or H2 as a fuel. We emphasise the techniques available for understanding detailed catalytic properties of the enzymes responsible for individual redox half-reactions, and the importance of a fundamental understanding of the enzyme characteristics in enabling effective applications of redox biocatalysis.