-
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.
-
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.
-
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.
-
4.
Fermentative Bio-Hydrogen Production of Food Waste in the Presence of Different Concentrations of Salt (Na+) and Nitrogen.
Lee, P, Hwang, Y, Lee, T
Journal of microbiology and biotechnology. 2019;(2):283-291
Abstract
Fermentation of food waste in the presence of different concentrations of salt (Na+) and ammonia was conducted to investigate the interrelation of Na+ and ammonia content in biohydrogen production. Analysis of the experimental results showed that peak hydrogen production differed according to the ammonia and Na+ concentration. The peak hydrogen production levels achieved were (97.60, 91.94, and 49.31) ml/g COD at (291.41, 768.75, and 1,037.89) mg-N/L of ammonia and (600, 1,000, and 4,000) mg-Na+/L of salt concentration, respectively. At peak hydrogen production, the ammonia concentration increased along with increasing salt concentration in the medium. This means that for peak hydrogen production, the C/N ratio decreased with increasing salt content in the medium. The butyrate/acetate (B/A) ratio was higher in proportion to the bio-hydrogen production (r-square: 0.71, p-value: 0.0006). Different concentrations of Na+ and ammonia in the medium also produced diverse microbial communities. Klebsiella sp., Enterobacter sp., and Clostridium sp. were predominant with high bio-hydrogen production, while Lactococcus sp. was found with low bio-hydrogen production.
-
5.
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.
-
6.
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.
-
7.
Hydrogen-rich water reduces liver fat accumulation and improves liver enzyme profiles in patients with non-alcoholic fatty liver disease: a randomized controlled pilot trial.
Korovljev, D, Stajer, V, Ostojic, J, LeBaron, TW, Ostojic, SM
Clinics and research in hepatology and gastroenterology. 2019;(6):688-693
Abstract
BACKGROUND AND AIMS While non-alcoholic fatty liver disease (NAFLD) is rapidly becoming the most common liver disease worldwide, its treatment remains elusive. Since metabolic impairment plays a major role in NAFLD pathogenesis, any pharmaceuticals, such as molecular hydrogen (H2), that advance lipid and glucose metabolism could be appropriate to tackle this complex condition. The aim of this study was to analyze the effects of 28-day hydrogen-rich water intake on liver fat deposition, body composition and lab chemistry profiles in overweight patients suffering from mild-to-moderate NAFLD. METHODS Twelve overweight outpatients with NAFLD (age 56.2 ± 10.0 years; body mass index 37.7 ± 5.3 kg/m2; 7 women and 5 men) voluntarily participated in this double-blind, placebo-controlled, crossover trial. All patients were allocated to receive either 1 L per day of hydrogen-rich water (HRW) or placebo water for 28 days. The study was registered at ClinicalTrials.gov (ID NCT03625362). RESULTS Dual-echo MRI revealed that HRW significantly reduced liver fat accumulation in individual liver regions-of-interest at 28-day follow-up, as compared to placebo administration (P < 0.05). Baseline liver fat content was reduced from 284.0 ± 118.1 mM to 256.5 ± 108.3 mM after hydrogen treatment at 28-day follow-up (percent change 2.9%; 95% CI from 0.5 to 5.5). Serum aspartate transaminase levels dropped by 10.0% (95% CI; from -23.2 to 3.4) after hydrogen treatment at 28-day follow-up. No significant differences were observed between treatment groups in either weight or body composition among participants. CONCLUSIONS Although preliminary, the results of this trial perhaps nominate HRW as an adjuvant treatment for mild-to-moderate NAFLD. These observations provide a rationale for further clinical trials to establish safety and efficacy of molecular hydrogen in NAFLD.
-
8.
Modeling alginate encapsulation system for biological hydrogen production.
Zhu, K, Arnold, WA, Novak, PJ
Biotechnology and bioengineering. 2019;(12):3189-3199
Abstract
Wastewater treatment using encapsulated biomass is a promising approach for high-rate resource recovery. Encapsulation matrices can be customized to achieve desired biomass retention and mass transport performance. This, in turn, facilitates treatment of different waste streams. In this study, a model was developed to describe calcium-alginate beads encapsulating hydrogen-producing biomass, with the goal of enabling appropriate a priori customization of the system. The model was based on a classic diffusion-reaction model, but also included the growth of encapsulated biomass and product inhibition. Experimental data were used to verify the model, which accurately described the effect of hydraulic retention time, bead size, and feed concentration on resource (hydrogen) recovery from brewery wastewater. Sensitivity analyses revealed that the hydrogen production rate was insensitive to substrate diffusivity and bead size, but sensitive to the substrate partition coefficient, initial encapsulated biomass concentration, and the total volume of beads in the reactor, demonstrating that this system was growth-limited rather than diffusion-limited under the tested conditions. Because the model quantifies the relationship between the hydrogen production rate and various input and operating parameters, it should be possible to extend the model to determine the most cost-effective system for optimal performance with a given waste stream.
-
9.
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.
-
10.
Two Chloroflexi classes independently evolved the ability to persist on atmospheric hydrogen and carbon monoxide.
Islam, ZF, Cordero, PRF, Feng, J, Chen, YJ, Bay, SK, Jirapanjawat, T, Gleadow, RM, Carere, CR, Stott, MB, Chiri, E, et al
The ISME journal. 2019;(7):1801-1813
-
-
Free full text
-
Abstract
Most aerobic bacteria exist in dormant states within natural environments. In these states, they endure adverse environmental conditions such as nutrient starvation by decreasing metabolic expenditure and using alternative energy sources. In this study, we investigated the energy sources that support persistence of two aerobic thermophilic strains of the environmentally widespread but understudied phylum Chloroflexi. A transcriptome study revealed that Thermomicrobium roseum (class Chloroflexia) extensively remodels its respiratory chain upon entry into stationary phase due to nutrient limitation. Whereas primary dehydrogenases associated with heterotrophic respiration were downregulated, putative operons encoding enzymes involved in molecular hydrogen (H2), carbon monoxide (CO), and sulfur compound oxidation were significantly upregulated. Gas chromatography and microsensor experiments showed that T. roseum aerobically respires H2 and CO at a range of environmentally relevant concentrations to sub-atmospheric levels. Phylogenetic analysis suggests that the hydrogenases and carbon monoxide dehydrogenases mediating these processes are widely distributed in Chloroflexi genomes and have probably been horizontally acquired on more than one occasion. Consistently, we confirmed that the sporulating isolate Thermogemmatispora sp. T81 (class Ktedonobacteria) also oxidises atmospheric H2 and CO during persistence, though further studies are required to determine if these findings extend to mesophilic strains. This study provides axenic culture evidence that atmospheric CO supports bacterial persistence and reports the third phylum, following Actinobacteria and Acidobacteria, to be experimentally shown to mediate the biogeochemically and ecologically important process of atmospheric H2 oxidation. This adds to the growing body of evidence that atmospheric trace gases are dependable energy sources for bacterial persistence.