Nitrate reduction to nitrite, nitric oxide and ammonia by gut bacteria under physiological conditions

Costless metabolic secretions as drivers of interspecies interactions in microbial ecosystems

Metabolic exchange mediates interactions among microbes, helping explain diversity in microbial communities. As these interactions often involve a fitness cost, it is unclear how stable cooperation can emerge. Here we use genome-scale metabolic models to investigate whether the release of “costless” metabolites (i.e. those that cause no fitness cost to the producer), can be a prominent driver of intermicrobial interactions. By performing over 2 million pairwise growth simulations of 24 species in a combinatorial assortment of environments, we identify a large space of metabolites that can be secreted without cost, thus generating ample cross-feeding opportunities. In addition to providing an atlas of putative interactions, we show that anoxic conditions can promote mutualisms by providing more opportunities for exchange of costless metabolites, resulting in an overrepresentation of stable ecological network motifs. These results may help identify interaction patterns in natural communities and inform the design of synthetic microbial consortia.

In considering cross-feeding among microbes within communities, it is typically assumed that metabolic secretions are costly to produce. However, Pacheco et al. use metabolic models to show that ‘costless’ secretions could be common in some environments and important for structuring interactions among microbes.

The role of the NADH-dependent nitrite reductase, Nir, from Escherichia coli in fermentative ammonification

Nitrate and nitrite reduction are of paramount importance for nitrogen assimilation and anaerobic metabolism, and understanding the specific roles of each participating reductase is necessary to describe the biochemical balance that dictates cellular responses to their environments. The soluble, cytoplasmic siroheme NADH-nitrite reductase (Nir) in Escherichia coli is necessary for nitrate/nitrite assimilation but has also been reported to either "detoxify" nitrite, or to carry out fermentative ammonification in support of anaerobic catabolism. Theoretically, nitrite detoxification would be important for anaerobic growth on nitrate, during which excess nitrite would be reduced to ammonium. Fermentative ammonification by Nir would be important for maximization of non-respiratory ATP production during anaerobic growth in the presence of nitrite. Experiments reported here were designed to test the potential role of Nir in fermentative ammonification directly by growing E. coli along with mutant strains lacking Nir or the respiratory nitrite reductase (Nrf) under anaerobic conditions in defined media while monitoring nitrogen utilization and fermentation metabolites. To focus on the role of Nir in fermentative ammonification, pH control was used in most experiments to eliminate nitrite toxicity due to nitric acid formation. Our results demonstrate that Nir confers a significant benefit during fermentative growth that reflects fermentative ammonification rather than detoxification. We conclude that fermentative ammonification by Nir allows for the energetically favorable fermentation of glucose to formate and acetate. These results and conclusions are discussed in light of the roles of Nir in other bacteria and in plants.

Exploring the physiological link of breath N2O through nitrification and denitrification processes in human gastric juice

Over the past several decades, it has been generally believed that microbial nitrification and denitrification are not significant processes in the human gastrointestinal tract. Moreover, the underlying physiological link between exhaled nitrous oxide (N₂O) and aerobic denitrification in the gastric environment is still largely unknown. In this report, we provide direct experimental evidence of the aerobic denitrification process in the human gastrointestinal tract by evaluating concentrations of dissolved N₂O and its precursor nitrite ([Formula: see text]) ion in the gastric juice along with exhaled N₂O concentration using a high-precision laser spectroscopy technique. Moreover, in vitro studies of gastric fluid in patients reveal a new mechanism of nitrification of ammonium ion ([Formula: see text]) followed by denitrification of [Formula: see text] leading to the formation of N₂O in the gastric environment, which is eventually excreted in exhaled breath. This observation was subsequently validated under in vivo physiological conditions exploiting the urease activity of the gastric pathogen Helicobacter pylori. Consequently, our findings established a strong physiological link between exhaled N₂O and bacterial infection in the stomach. This deepens our understanding of the unusual microbial denitrification in the gastric environment, providing new insight into the activities of human-associated microorganisms, which eventually affect the human physiology and health.

Copepod-Associated Gammaproteobacteria Respire Nitrate in the Open Ocean Surface Layers

Microbial dissimilatory nitrate reduction to nitrite, or nitrate respiration, was detected in association with copepods in the oxygenated water column of the North Atlantic subtropical waters. These unexpected rates correspond to up to 0.09 nmol N copepod-1 d-1 and demonstrate a previously unaccounted nitrogen transformation in the oceanic pelagic surface layers. Genes and transcripts for both the periplasmic and membrane associated dissimilatory nitrate reduction pathways (Nap and Nar, respectively) were detected. The napA genes and transcripts were closely related with sequences from several clades of Vibrio sp., while the closest relatives of the narG sequences were Pseudoalteromonas spp. and Alteromonas spp., many of them representing clades only distantly related to previously described cultivated bacteria. The discovered activity demonstrates a novel Gammaproteobacterial respiratory role in copepod association, presumably providing energy for these facultatively anaerobic bacteria, while supporting a reductive path of nitrogen in the oxygenated water column of the open ocean.

Effects of Beetroot Juice Supplementation on Performance and Fatigue in a 30-s All-Out Sprint Exercise: A Randomized, Double-Blind Cross-Over Study

As a nitric oxide precursor, beetroot juice (BJ) is known to enhance high-intensity exercise performance (80⁻100% VO2max) yet its impacts on higher intensity sprint exercise (>100% VO2max) remain to be established. This study sought to examine the effects of BJ supplementation on performance and subsequent fatigue during an all-out sprint exercise. Using a randomized cross-over, double-blind, placebo-controlled design, 15 healthy resistance-trained men (22.4 ± 1.6 years) ingested 70 mL of either BJ or placebo. Three hours later, participants undertook a 30-s all-out Wingate test. Before and after the sprint exercise and at 30 s and 180 s post-exercise, three countermovement jumps (CMJ) were performed and blood lactate samples were obtained. Compared to placebo, BJ consumption improved peak (placebo vs. BJ, 848 ± 134 vs. 881 ± 135 W; p = 0.049) and mean (641 ± 91 vs. 666 ± 100 W; p = 0.023) power output and also reduced the time taken to reach Wpeak in the Wingate test (8.9 ± 1.4 vs. 7.3 ± 0.9 s; p = 0.003). No differences were detected in the fatigue index. In addition, while over time CMJ height and power diminished (ANOVA p < 0.001) and blood lactate levels increased (ANOVA p < 0.001), no supplementation effect was observed. Our findings indicate that while BJ supplementation improved performance at the 30-s cycling sprint, this improvement was not accompanied by differences in fatigue during or after this type of exercise.

Reproductive endocrinology of environmental nitrate

Nitrate is a widespread contaminant of aquatic ecosystems and drinking water. It is also broadly active in organismal physiology, and as such, has the potential to both enhance and disrupt normal physiological function. In animals, nitrate is a proposed endocrine disrupter that is converted in vivo to nitrite and nitric oxide. Nitric oxide, in particular, is a potent cell signaling molecule that participates in diverse biological pathways and events. Here, we review in vivo nitrate cycling and downstream mechanistic physiology, with an emphasis on reproductive outcomes. However, in many cases, the research produces contradictory results, in part because there is good evidence that nitrate follows a non-monotonic dose-response curve. This conundrum highlights an array of opportunities for scientists from different fields to collaborate for a full understanding of nitrate physiology. Opposing conclusions are especially likely when in vivo/in vitro, long term/short term, high dose/low dose, or hypoxia/normoxia studies are compared. We conclude that in vivo studies are most appropriate for testing an organism's integrated endocrine response to nitrate. Based on the limited available studies, there is a generalized trend that shorter term studies (less than 1 month) or studies involving low doses (≤5 mg/L NO₃-N) cause steroid hormone levels to decline. Studies that last more than a month and/or involve higher, but still environmentally relevant, exposures (>50-100 mg/L NO₃-N) cause steroid hormone levels to increase. Very high nitrate doses (>500 mg/L NO₃-N) are cytotoxic in many species. Hypoxia and acidity are likely to intensify the effects of nitrate. For study design, degree of study animal reproductive maturity or activity is important, with immature/reproductively quiescent animals responding to nitrate differently, compared with reproductively active animals. A detailed table of studies is presented.

Mechanisms underlying blood pressure reduction by dietary inorganic nitrate

Nitric oxide (NO) importantly contributes to cardiovascular homeostasis by regulating blood flow and maintaining endothelial integrity. Conversely, reduced NO bioavailability is a central feature during natural ageing and in many cardiovascular disorders, including hypertension. The inorganic anions nitrate and nitrite are endogenously formed after oxidation of NO synthase (NOS)-derived NO and are also present in our daily diet. Knowledge accumulated over the past two decades has demonstrated that these anions can be recycled back to NO and other bioactive nitrogen oxides via serial reductions that involve oral commensal bacteria and various enzymatic systems. Intake of inorganic nitrate, which is predominantly found in green leafy vegetables and beets, has a variety of favourable cardiovascular effects. As hypertension is a major risk factor of morbidity and mortality worldwide, much attention has been paid to the blood pressure reducing effect of inorganic nitrate. Here, we describe how dietary nitrate, via stimulation of the nitrate-nitrite-NO pathway, affects various organ systems and discuss underlying mechanisms that may contribute to the observed blood pressure-lowering effect.

NADPH oxidases and ROS signaling in the gastrointestinal tract

Reactive oxygen species (ROS), initially categorized as toxic by-products of aerobic metabolism, have often been called a double-edged sword. ROS are considered indispensable when host defense and redox signaling is concerned and a threat in inflammatory or degenerative diseases. This generalization does not take in account the diversity of oxygen metabolites being generated, their physicochemical characteristics and their production by distinct enzymes in space and time. NOX/DUOX NADPH oxidases are the only enzymes solely dedicated to ROS production and the prime ROS producer for intracellular and intercellular communication due to their widespread expression and intricate regulation. Here we discuss new insights of how NADPH oxidases act via ROS as multifaceted regulators of the intestinal barrier in homeostasis, infectious disease and intestinal inflammation. A closer look at monogenic VEOIBD and commensals as ROS source supports the view of H₂O₂ as key beneficial messenger in the barrier ecosystem.

Influence of the Potential Carbon Sources for Field Denitrification Beds on Their Microbial Diversity and the Fate of Carbon and Nitrate

Nitrogen based eutrophication of ecosystems is a global problem that gains momentum through a growing global population. The water quality of nitrate or ammonium contaminated rivers and streams cannot always be amended in centralized waste water treatment plants. Field denitrification plants were suggested as a solution for a decentralized reduction of nitrate to dinitrogen. Here, stable and cheap organic carbon sources serve as carbon and electron source for a microbial community. Still, our knowledge on the impact of these organic carbon sources on the development and diversity of these cultures is sparse. Moreover, the stability of these denitrification plants at different nitrate loading rates especially in the higher concentration regime were not tested so far. In this study, we compare the fate of carbon and nitrogen as well as the microbial community of wood pellet (WP) (pressed sawdust), wheat straw, and wood chips (WC) based laboratory denitrification reactors. Our study reveals that the diversity and composition of the community is strongly dependent on the carbon source. The diversity decreased in the order WC, wheat straw, and WPs. The three reactor types were characterized by different nitrate reduction kinetics and were affected differently by high nitrate loading rates. While the nitrate reduction kinetics were negatively influenced by higher nitrate doses in the wheat straw reactors, WPs as carbon source sustained the opposite trend and WC lead to an overall slower but concentration independent nitrate reduction rate. Counterintuitively, the concentration of soluble organic carbon was highest in the WP reactors but methane emission was not detectable. This is corroborated by the microbial diversity data in which methanogenic species were highly underrepresented compared to the other two reactor types. In contrary, the methane emissions in the wheat straw and WC reactors were comparable to each other.

Proteomic analysis of the response of Trichinella spiralis muscle larvae to exogenous nitric oxide

Trichinella spiralis mainly dwells in the muscle tissue of its host and is the main causative agent of trichinellosis in humans. Nitric oxide (NO), an important intracellular signaling molecule that may restrict pathogen growth in infected hosts, has been known for its anti-pathogenic activity, including resistance to T. spiralis. Herein, we applied label-free analysis to investigate the effect of sodium nitroprusside (SNP, a NO donor compound) on the proteome of T. spiralis muscle larvae (ML), followed by Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway cluster analyses. Of the 1,476 proteins detected in the ML, 121 proteins showed differential expression, including 50 significantly upregulated and 71 downregulated proteins. The functions of the 108 annotated proteins were primarily related to signal transduction, transcription/translation, material metabolism, protein synthesis/assembly/degradation, and stress/defense/antioxidation. Quantitative real-time polymerase chain reaction (qRT-PCR) assay verified that FRMD5 and CUT-1 gene expression levels were significantly increased, while COX2 gene expression level was significantly decreased. GO annotation and KEGG pathway analyses showed that the majority of differentially expressed proteins were mainly involved in the molecular function of the catalytic activity, biological process of the immune system process, metabolic process, cellular component organization, biological adhesion, and cellular component of the macromolecular complex. Our results demonstrate the first comprehensive protein expression profile of the ML in response to NO stress and provide novel references for understanding the potential mechanism underlying the effects of NO on trichinellosis.

Nitrate: An Environmental Endocrine Disruptor? A Review of Evidence and Research Needs

Nitrate is heavily used as an agricultural fertilizer and is today a ubiquitous environmental pollutant. Environmental endocrine effects caused by nitrate have received increasing attention over the last 15 years. Nitrate is hypothesized to interfere with thyroid and steroid hormone homeostasis and developmental and reproductive end points. The current review focuses on aquatic ecotoxicology with emphasis on field and laboratory controlled in vitro and in vivo studies. Furthermore, nitrate is just one of several forms of nitrogen that is present in the environment and many of these are quickly interconvertible. Therefore, the focus is additionally confined to the oxidized nitrogen species (nitrate, nitrite and nitric oxide). We reviewed 26 environmental toxicology studies and our main findings are (1) nitrate has endocrine disrupting properties and hypotheses for mechanisms exist, which warrants for further investigations; (2) there are issues determining actual nitrate-speciation and abundance is not quantified in a number of studies, making links to speciation-specific effects difficult; and (3) more advanced analytical chemistry methodologies are needed both for exposure assessment and in the determination of endocrine biomarkers.

Genomic and physiological analyses of an indigenous strain, Enterococcus faecium 17OM39

The human gut microbiome plays a crucial role in human health and efforts need to be done for cultivation and characterisation of bacteria with potential health benefits. Here, we isolated a bacterium from a healthy Indian adult faeces and investigated its potential as probiotic. The cultured bacterial strain 17OM39 was identified as Enterococcus faecium by 16S rRNA gene sequencing. The strain 17OM39 exhibited tolerance to acidic pH, showed antimicrobial activity and displayed strong cell surface traits such as hydrophobicity and autoaggregation capacity. The strain was able to tolerate bile salts and showed bile salt hydrolytic (BSH) activity, exopolysaccharide production and adherence to human HT-29 cell line. Importantly, partial haemolytic activity was detected and the strain was susceptible to the human serum. Genomics investigation of strain 17OM39 revealed the presence of diverse genes encoding for proteolytic enzymes, stress response systems and the ability to produce essential amino acids, vitamins and antimicrobial compound Bacteriocin-A. No virulence factors and plasmids were found in this genome of the strain 17OM39. Collectively, these physiological and genomic features of 17OM39 confirm the potential of this strain as a candidate probiotic.

The effects of two different doses of ultraviolet-A light exposure on nitric oxide metabolites and cardiorespiratory outcomes

Purpose

The present study investigated different doses of ultraviolet-A (UV-A) light on plasma nitric oxide metabolites and cardiorespiratory variables.

Methods

Ten healthy male participants completed three experimental conditions, 7 days apart. Participants were exposed to no light (CON); 10 J cm² (15 min) of UV-A light (UVA10) and 20 J cm² (30 min) of UV-A light (UVA20) in a randomized order. Plasma nitrite [NO₂⁻] and nitrate [NO₃⁻] concentrations, blood pressure (BP), and heart rate (HR) were recorded before, immediately after exposure and 30 min post-exposure. Whole body oxygen utilization (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2), resting metabolic rate (RMR) and skin temperature were recorded continuously.

Results

None of the measured parameters changed significantly during CON (all P > 0.05). \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR were significantly reduced immediately after UVA10 (P < 0.05) despite no change in plasma [NO₂⁻] (P > 0.05). Immediately after exposure to UVA20, plasma [NO₂⁻] was higher (P = 0.014) and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR tended to be lower compared to baseline (P = 0.06). There were no differences in [NO₂⁻] or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 at the 30 min time point in any condition. UV-A exposure did not alter systolic BP, diastolic BP or MAP (all P > 0.05). UV-A light did not alter plasma [NO₃⁻] at any time point (all P > 0.05).

Conclusions

This study demonstrates that a UV-A dose of 20 J cm² is necessary to increase plasma [NO₂⁻] although a smaller dose is capable of reducing \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR at rest. Exposure to UV-A did not significantly reduce BP in this cohort of healthy adults. These data suggest that exposure to sunlight has a meaningful acute impact on metabolic function.

Fat accretion measurements strengthen the relationship between feed conversion efficiency and Nitrogen isotopic discrimination while rumen microbial genes contribute little

The use of biomarkers for feed conversion efficiency (FCE), such as Nitrogen isotopic discrimination (Δ15N), facilitates easier measurement and may be useful in breeding strategies. However, we need to better understand the relationship between FCE and Δ15N, particularly the effects of differences in the composition of liveweight gain and rumen N metabolism. Alongside measurements of FCE and Δ15N, we estimated changes in body composition and used dietary treatments with and without nitrates, and rumen metagenomics to explore these effects. Nitrate fed steers had reduced FCE and higher Δ15N in plasma compared to steers offered non-nitrate containing diets. The negative relationship between FCE and Δ15N was strengthened with the inclusion of fat depth change at the 3rd lumbar vertebrae, but not with average daily gain. We identified 1,700 microbial genes with a relative abundance >0.01% of which, 26 were associated with Δ15N. These genes explained 69% of variation in Δ15N and showed clustering in two distinct functional networks. However, there was no clear relationship between their relative abundances and Δ15N, suggesting that rumen microbial genes contribute little to Δ15N. Conversely, we show that changes in the composition of gain (fat accretion) provide additional strength to the relationship between FCE and Δ15N.

Structure of a Wbl protein and implications for NO sensing by M. tuberculosis

Mycobacterium tuberculosis causes pulmonary tuberculosis (TB) and claims ~1.8 million human lives per annum. Host nitric oxide (NO) is important in controlling TB infection. M. tuberculosis WhiB1 is a NO-responsive Wbl protein (actinobacterial iron–sulfur proteins first identified in the 1970s). Until now, the structure of a Wbl protein has not been available. Here a NMR structural model of WhiB1 reveals that Wbl proteins are four-helix bundles with a core of three α-helices held together by a [4Fe-4S] cluster. The iron–sulfur cluster is required for formation of a complex with the major sigma factor (σ^A) and reaction with NO disassembles this complex. The WhiB1 structure suggests that loss of the iron–sulfur cluster (by nitrosylation) permits positively charged residues in the C-terminal helix to engage in DNA binding, triggering a major reprogramming of gene expression that includes components of the virulence-critical ESX-1 secretion system.

Mycobacterium tuberculosis WhiB1 is a DNA-binding protein with a NO sensitive [4Fe-4S] cluster. Here the authors present the NMR structure of WhiB1 and suggest how loss of the iron-sulfur cluster through nitrosylation affects WhiB1 DNA binding and leads to transcriptional reprogramming.

Underexplored microbial metabolisms for enhanced nutrient recycling in agricultural soils

Worldwide, arable soils have been degraded through erosion and exhaustive cultivation, and substantial proportions of fertilizer nutrients are not taken up by crops. A central challenge in agriculture is to understand how soils and resident microbial communities can be managed to deliver nutrients to crops more efficiently with minimal losses to the environment. Throughout much of the twentieth century, intensive farming has caused substantial loss of organic matter and soil biological function. Today, more farmers recognize the importance of protecting soils and restoring organic matter through reduced tillage, diversified crop rotation, cover cropping, and increased organic amendments. Such management practices are expected to foster soil conditions more similar to those of undisturbed, native plant-soil systems by restoring soil biophysical integrity and re-establishing plant-microbe interactions that retain and recycle nutrients. Soil conditions which could contribute to desirable shifts in microbial metabolic processes include lower redox potentials, more diverse biogeochemical gradients, higher concentrations of labile carbon, and enrichment of carbon dioxide (CO2) and hydrogen gas (H2) in soil pores. This paper reviews recent literature on generalized and specific microbial processes that could become more operational once soils are no longer subjected to intensive tillage and organic matter depletion. These processes include heterotrophic assimilation of CO2; utilization of H2 as electron donor or reactant; and more diversified nitrogen uptake and dissimilation pathways. Despite knowledge of these processes occurring in laboratory studies, they have received little attention for their potential to affect nutrient and energy flows in soils. This paper explores how soil microbial processes could contribute to in situ nutrient retention, recycling, and crop uptake in agricultural soils managed for improved biological function.

The role of nitric oxide in melanoma

Nitric oxide (NO) is a small gaseous signaling molecule that mediates its effects in melanoma through free radical formation and enzymatic processes. Investigations have demonstrated multiple roles for NO in melanoma pathology via immune surveillance, apoptosis, angiogenesis, melanogenesis, and on the melanoma cell itself. In general, elevated levels of NO prognosticate a poor outcome for melanoma patients. However, there are processes where the relative concentration of NO in different environments may also serve to limit melanoma proliferation. This review serves to outline the roles of NO in melanoma development and proliferation. As demonstrated by multiple in vivo murine models and observations from human tissue, NO may promote melanoma formation and proliferation through its interaction via inhibitory immune cells, inhibition of apoptosis, stimulation of pro-tumorigenic cytokines, activation of tumor associated macrophages, alteration of angiogenic processes, and stimulation of melanoma formation itself.

A 13-week low glycemic load diet and lifestyle modification program combining low glycemic load protein shakes and targeted nutraceuticals improved weight loss and cardio-metabolic risk factors

An open-label, randomized, exploratory study of 44 healthy overweight subjects with cardio-metabolic syndrome (CMS) risk factors was conducted to assess the safety, tolerability, and efficacy of a proprietary lifestyle modification program without (DIET) and with (PROG) targeted nutraceutical supplementation, including phytosterols, antioxidants, probiotics, fish oil, berberine, and soy, pea, and whey proteins over 13 weeks. Key metrics were recorded at baseline and weeks 9 and 13. For the DIET and PROG groups, compliance was 85% and 86%, respectively, with no adverse events related to the diet or supplements. Twelve subjects discontinued participation before week 9 for reasons unrelated to the study. PROG subjects experienced greater decreases (p < 0.05) than DIET in body mass, fat mass, total cholesterol, LDL cholesterol, TG, cholesterol / HDL ratio, TG/HDL ratio, apolipoprotein B / apolipoprotein A1 ratio, and hs-CRP. The Framingham 10-year cardiovascular disease risk score decreased by 40% (p < 0.01) in the PROG arm versus no change for the DIET arm. As a pilot study, it was not possible to state whether the observed effects were the result of nutraceutical supplementation alone or the result of additive or synergistic interactions among diet, lifestyle modifications, and nutraceutical supplementation. Moreover, individuals with CMS risk factors following a lifestyle modification program received additional health benefits from targeted nutraceutical supplementation.

Bacteria-mediated hypoxia functions as a signal for mosquito development

Mosquitoes host communities of microbes in their digestive tract that consist primarily of bacteria. We previously reported that several mosquito species, including Aedes aegypti, do not develop beyond the first instar when fed a nutritionally complete diet in the absence of a gut microbiota. In contrast, several species of bacteria, including Escherichia coli, rescue development of axenic larvae into adults. The molecular mechanisms underlying bacteria-dependent growth are unknown. Here, we designed a genetic screen around E. coli that identified high-affinity cytochrome bd oxidase as an essential bacterial gene product for mosquito growth. Bioassays showed that bacteria in nonsterile larvae and gnotobiotic larvae inoculated with wild-type E. coli reduced midgut oxygen levels below 5%, whereas larvae inoculated with E. coli mutants defective for cytochrome bd oxidase did not. Experiments further supported that hypoxia leads to growth and ecdysone-induced molting. Altogether, our results identify aerobic respiration by bacteria as a previously unknown but essential process for mosquito development.

Health benefit of vegetable/fruit juice-based diet: Role of microbiome

The gut microbiota is an important contributor to human health. Vegetable/fruit juices provide polyphenols, oligosaccharides, fiber and nitrate (beet juice), which may induce a prebiotic-like effect. Juice-based diets are becoming popular. However, there is a lack of scientific evidence of their health benefits. It was our hypothesis that changes in the intestinal microbiota induced by a juice-based diet play an important role in their health benefits. Twenty healthy adults consumed only vegetable/fruit juices for 3 days followed by 14 days of customary diet. On day 4 we observed a significant decrease in weight and body mass index (p = 2.0E⁻⁰⁵), which was maintained until day 17 (p = 3.0E⁻⁰⁴). On day 4 the proportion of the phylum Firmicutes and Proteobacteria in stool was significantly decreased and Bacteroidetes and Cyanobacteria was increased compared to baseline and was partially reversed on day 17. On day 4 plasma and urine nitric oxide was increased by 244 ± 89% and 450 ± 360%, respectively, and urinary lipid peroxidation marker malondialdehyde was decreased by 32 ± 21% compared to baseline. General well-being score was increased at the end of the study. In summary a 3-day juice-based diet altered the intestinal microbiota associated with weight loss, increase in the vasodilator NO, and decrease in lipid oxidation.

Pterin function in bacteria

Pterins are widely conserved biomolecules that play essential roles in diverse organisms. First described as enzymatic cofactors in eukaryotic systems, bacterial pterins were discovered in cyanobacteria soon after. Several pterin structures unique to bacteria have been described, with conjugation to glycosides and nucleotides commonly observed. Despite this significant structural diversity, relatively few biological functions have been elucidated. Molybdopterin, the best studied bacterial pterin, plays an essential role in the function of the Moco cofactor. Moco is an essential component of molybdoenzymes such as sulfite oxidase, nitrate reductase, and dimethyl sulfoxide reductase, all of which play important roles in bacterial metabolism and global nutrient cycles. Outside of the molybdoenzymes, pterin cofactors play important roles in bacterial cyanide utilization and aromatic amino acid metabolism. Less is known about the roles of pterins in nonenzymatic processes. Cyanobacterial pterins have been implicated in phenotypes related to UV protection and phototaxis. Research describing the pterin-mediated control of cyclic nucleotide metabolism, and their influence on virulence and attachment, points to a possible role for pterins in regulation of bacterial behavior. In this review, we describe the variety of pterin functions in bacteria, compare and contrast structural and mechanistic differences, and illuminate promising avenues of future research.

Enterosalivary nitrate metabolism and the microbiome: Intersection of microbial metabolism, nitric oxide and diet in cardiac and pulmonary vascular health

Recent insights into the bioactivation and signaling actions of inorganic, dietary nitrate and nitrite now suggest a critical role for the microbiome in the development of cardiac and pulmonary vascular diseases. Once thought to be the inert, end-products of endothelial-derived nitric oxide (NO) heme-oxidation, nitrate and nitrite are now considered major sources of exogenous NO that exhibit enhanced vasoactive signaling activity under conditions of hypoxia and stress. The bioavailability of nitrate and nitrite depend on the enzymatic reduction of nitrate to nitrite by a unique set of bacterial nitrate reductase enzymes possessed by specific bacterial populations in the mammalian mouth and gut. The pathogenesis of pulmonary hypertension (PH), obesity, hypertension and CVD are linked to defects in NO signaling, suggesting a role for commensal oral bacteria to shape the development of PH through the formation of nitrite, NO and other bioactive nitrogen oxides. Oral supplementation with inorganic nitrate or nitrate-containing foods exert pleiotropic, beneficial vascular effects in the setting of inflammation, endothelial dysfunction, ischemia-reperfusion injury and in pre-clinical models of PH, while traditional high-nitrate dietary patterns are associated with beneficial outcomes in hypertension, obesity and CVD. These observations highlight the potential of the microbiome in the development of novel nitrate- and nitrite-based therapeutics for PH, CVD and their risk factors.

An update on the use of benzoate, phenylacetate and phenylbutyrate ammonia scavengers for interrogating and modifying liver nitrogen metabolism and its implications in urea cycle disorders and liver disease

INTRODUCTION

Ammonia-scavenging drugs, benzoate and phenylacetate (PA)/phenylbutyrate (PB), modulate hepatic nitrogen metabolism mainly by providing alternative pathways for nitrogen disposal. Areas covered: We review the major findings and potential novel applications of ammonia-scavenging drugs, focusing on urea cycle disorders and liver disease. Expert opinion: For over 40 years, ammonia-scavenging drugs have been used in the treatment of urea cycle disorders. Recently, the use of these compounds has been advocated in acute liver failure and cirrhosis for reducing hyperammonemic-induced hepatic encephalopathy. The efficacy and mechanisms underlying the antitumor effects of these ammonia-scavenging drugs in liver cancer are more controversial and are discussed in the review. Overall, as ammonia-scavenging drugs are usually safe and well tolerated among cancer patients, further studies should be instigated to explore the role of these drugs in liver cancer. Considering the relevance of glutamine metabolism to the progression and resolution of liver disease, we propose that ammonia-scavenging drugs might also be used to non-invasively probe liver glutamine metabolism in vivo. Finally, novel derivatives of classical ammonia-scavenging drugs with fewer and less severe adverse effects are currently being developed and used in clinical trials for the treatment of acute liver failure and cirrhosis.

Recent insights into nitrite signaling processes in blood

Nitrite was once thought to be inert in human physiology. However, research over the past few decades has established a link between nitrite and the production of nitric oxide (NO) that is potentiated under hypoxic and acidic conditions. Under this new role nitrite acts as a storage pool for bioavailable NO. The NO so produced is likely to play important roles in decreasing platelet activation, contributing to hypoxic vasodilation and minimizing blood-cell adhesion to endothelial cells. Researchers have proposed multiple mechanisms for nitrite reduction in the blood. However, NO production in blood must somehow overcome rapid scavenging by hemoglobin in order to be effective. Here we review the role of red blood cell hemoglobin in the reduction of nitrite and present recent research into mechanisms that may allow nitric oxide and other reactive nitrogen signaling species to escape the red blood cell.

Lifestyle and Horizontal Gene Transfer-Mediated Evolution of Mucispirillum schaedleri, a Core Member of the Murine Gut Microbiota

Shifts in gut microbiota composition have been associated with intestinal inflammation, but it remains unclear whether inflammation-associated bacteria are commensal or detrimental to their host. Here, we studied the lifestyle of the gut bacterium Mucispirillum schaedleri, which is associated with inflammation in widely used mouse models. We found that M. schaedleri has specialized systems to handle oxidative stress during inflammation. Additionally, it expresses secretion systems and effector proteins and can modify the mucosal gene expression of its host. This suggests that M. schaedleri undergoes intimate interactions with its host and may play a role in inflammation. The insights presented here aid our understanding of how commensal gut bacteria may be involved in altering susceptibility to disease.

Mucispirillum schaedleri is an abundant inhabitant of the intestinal mucus layer of rodents and other animals and has been suggested to be a pathobiont, a commensal that plays a role in disease. In order to gain insights into its lifestyle, we analyzed the genome and transcriptome of M. schaedleri ASF 457 and performed physiological experiments to test traits predicted by its genome. Although described as a mucus inhabitant, M. schaedleri has limited capacity for degrading host-derived mucosal glycans and other complex polysaccharides. Additionally, M. schaedleri reduces nitrate and expresses systems for scavenging oxygen and reactive oxygen species in vivo, which may account for its localization close to the mucosal tissue and expansion during inflammation. Also of note, M. schaedleri harbors a type VI secretion system and putative effector proteins and can modify gene expression in mucosal tissue, suggesting intimate interactions with its host and a possible role in inflammation. The M. schaedleri genome has been shaped by extensive horizontal gene transfer, primarily from intestinal Epsilon- and Deltaproteobacteria, indicating that horizontal gene transfer has played a key role in defining its niche in the gut ecosystem.

IMPORTANCE Shifts in gut microbiota composition have been associated with intestinal inflammation, but it remains unclear whether inflammation-associated bacteria are commensal or detrimental to their host. Here, we studied the lifestyle of the gut bacterium Mucispirillum schaedleri, which is associated with inflammation in widely used mouse models. We found that M. schaedleri has specialized systems to handle oxidative stress during inflammation. Additionally, it expresses secretion systems and effector proteins and can modify the mucosal gene expression of its host. This suggests that M. schaedleri undergoes intimate interactions with its host and may play a role in inflammation. The insights presented here aid our understanding of how commensal gut bacteria may be involved in altering susceptibility to disease.

Intestinal microbiota as a tetrahydrobiopterin exogenous source in hph-1 mice

Tetrahydrobiopterin (BH4) is a cofactor of a number of regulatory enzymes. Although there are no known BH4 exogenous sources, the tissue content of this biopterin increases with age in GTP cyclohydrolase 1-deficient hyperphenylalaninemia-1 (hph-1) mice. Since certain bacteria are known to generate BH4, we hypothesize that generation of this biopterin by the intestinal microbiota contributes to its tissue increase in hph-1 adult mice. The goal of this study was to comparatively evaluate hph-1 mice and wild-type C57Bl/6 controls for the presence of intestinal BH4-producing bacteria. Newborn and adult mice fecal material was screened for 6-pyruvoyltetrahydropterin synthase (PTPS-2) an enzyme only present in BH4-generating bacteria. Adult, but not newborn, wild-type control and hph-1 mouse fecal material contained PTPS-2 mRNA indicative of the presence of BH4-generating bacteria. Utilizing chemostat-cultured human fecal bacteria, we identified the PTPS-2-producing bacteria as belonging to the Actinobacteria phylum. We further confirmed that at least two PTPS-2-producing species, Aldercreutzia equolifaciens and Microbacterium schleiferi, generate BH4 and are present in hph-1 fecal material. In conclusion, intestinal Actinobacteria generate BH4. This finding has important translational significance, since manipulation of the intestinal flora in individuals with congenital biopterin deficiency may allow for an increase in total body BH4 content.

Gut Bacteria and Hydrogen Sulfide: The New Old Players in Circulatory System Homeostasis

Accumulating evidence suggests that gut bacteria play a role in homeostasis of the circulatory system in mammals. First, gut bacteria may affect the nervous control of the circulatory system via the sensory fibres of the enteric nervous system. Second, gut bacteria-derived metabolites may cross the gut-blood barrier and target blood vessels, the heart and other organs involved in the regulation of the circulatory system. A number of studies have shown that hydrogen sulfide (H₂S) is an important biological mediator in the circulatory system. Thus far, research has focused on the effects of H₂S enzymatically produced by cardiovascular tissues. However, some recent evidence indicates that H₂S released in the colon may also contribute to the control of arterial blood pressure. Incidentally, sulfate-reducing bacteria are ubiquitous in mammalian colon, and H₂S is just one among a number of molecules produced by the gut flora. Other gut bacteria-derived compounds that may affect the circulatory system include methane, nitric oxide, carbon monoxide, trimethylamine or indole. In this paper, we review studies that imply a role of gut microbiota and their metabolites, such as H₂S, in circulatory system homeostasis.

Natural Products for the Treatment of Chlamydiaceae Infections

Due to the global prevalence of Chlamydiae, exploring studies of diverse antichlamydial compounds is important in the development of effective treatment strategies and global infectious disease management. Chlamydiaceae is the most widely known bacterial family of the Chlamydiae order. Among the species in the family Chlamydiaceae, Chlamydia trachomatis and Chlamydia pneumoniae cause common human diseases, while Chlamydia abortus, Chlamydia psittaci, and Chlamydia suis represent zoonotic threats or are endemic in human food sources. Although chlamydial infections are currently manageable in human populations, chlamydial infections in livestock are endemic and there is significant difficulty achieving effective treatment. To combat the spread of Chlamydiaceae in humans and other hosts, improved methods for treatment and prevention of infection are needed. There exist various studies exploring the potential of natural products for developing new antichlamydial treatment modalities. Polyphenolic compounds can inhibit chlamydial growth by membrane disruption, reestablishment of host cell apoptosis, or improving host immune system detection. Fatty acids, monoglycerides, and lipids can disrupt the cell membranes of infective chlamydial elementary bodies (EBs). Peptides can disrupt the cell membranes of chlamydial EBs, and transferrins can inhibit chlamydial EBs from attachment to and permeation through the membranes of host cells. Cellular metabolites and probiotic bacteria can inhibit chlamydial infection by modulating host immune responses and directly inhibiting chlamydial growth. Finally, early stage clinical trials indicate that polyherbal formulations can be effective in treating chlamydial infections. Herein, we review an important body of literature in the field of antichlamydial research.

The emerging role of gasotransmitters in the pathogenesis of tuberculosis

Mycobacterium tuberculosis (Mtb) is a facultative intracellular pathogen and the second largest contributor to global mortality caused by an infectious agent after HIV. In infected host cells, Mtb is faced with a harsh intracellular environment including hypoxia and the release of nitric oxide (NO) and carbon monoxide (CO) by immune cells. Hypoxia, NO and CO induce a state of in vitro dormancy where Mtb senses these gases via the DosS and DosT heme sensor kinase proteins, which in turn induce a set of ∼47 genes, known as the Mtb Dos dormancy regulon. On the contrary, both iNOS and HO-1, which produce NO and CO, respectively, have been shown to be important against mycobacterial disease progression. In this review, we discuss the impact of O2, NO and CO on Mtb physiology and in host responses to Mtb infection as well as the potential role of another major endogenous gas, hydrogen sulfide (H2S), in Mtb pathogenesis.

A tale of two sites: how inflammation can reshape the microbiomes of the gut and lungs

Inflammation can directly and indirectly modulate the bacterial composition of the microbiome. Although studies of inflammation primarily focus on its function to negatively select against potential pathogens, some bacterial species have the ability to exploit inflammatory byproducts for their benefit. Inflammatory cells release reactive nitrogen species as antimicrobial effectors against infection, but some facultative anaerobes can also utilize the increase in extracellular nitrate in their environment for anaerobic respiration and growth. This phenomenon has been studied in the gastrointestinal tract, where blooms of facultative anaerobic Gammaproteobacteria, primarily Escherichia coli, often occur during colonic inflammation. In cystic fibrosis, Pseudomonas aeruginosa, another Gammaproteobacteria facultative anaerobe, can reduce nitrogen for anaerobic respiration and it blooms in the airways of the chronically inflamed cystic fibrosis lung. This review focuses on the evidence that inflammation can provide terminal electron acceptors for anaerobic respiration and can support blooms of facultative anaerobes, such as E. coli and P. aeruginosa in distinct, but similar, environments of the inflamed gastrointestinal and respiratory tracts.

Is beetroot juice more effective than sodium nitrate? The effects of equimolar nitrate dosages of nitrate-rich beetroot juice and sodium nitrate on oxygen consumption during exercise

Dietary nitrate has been reported to lower oxygen consumption in moderate- and severe-intensity exercise. To date, it is unproven that sodium nitrate (NaNO3(-); NIT) and nitrate-rich beetroot juice (BR) have the same effects on oxygen consumption, blood pressure, and plasma nitrate and nitrite concentrations or not. The aim of this study was to compare the effects of different dosages of NIT and BR on oxygen consumption in male athletes. Twelve healthy, well-trained men (median [minimum; maximum]; peak oxygen consumption: 59.4 mL·min(-1)·kg(-1) [40.5; 67.0]) performed 7 trials on different days, ingesting different nitrate dosages and placebo (PLC). Dosages were 3, 6, and 12 mmol nitrate as concentrated BR or NIT dissolved in plain water. Plasma nitrate and nitrite concentrations were measured before, 3 h after ingestion, and postexercise. Participants cycled for 5 min at moderate intensity and further 8 min at severe intensity. End-exercise oxygen consumption at moderate intensity was not significantly different between the 7 trials (p = 0.08). At severe-intensity exercise, end-exercise oxygen consumption was ~4% lower in the 6-mmol BR trial compared with the 6-mmol NIT (p = 0.003) trial as well as compared with PLC (p = 0.010). Plasma nitrite and nitrate concentrations were significantly increased after the ingestion of BR and NIT with the highest concentrations in the 12-mmol trials. Plasma nitrite concentration between NIT and BR did not significantly differ in the 6-mmol (p = 0.27) and in the 12-mmol (p = 0.75) trials. In conclusion, BR might reduce oxygen consumption to a greater extent compared with NIT.

Clinical and pathophysiological consequences of alterations in the microbiome in cirrhosis

Cirrhosis is a major cause of mortality worldwide. Exponential rises in prevalence have been observed secondary to increases in obesity and alcohol consumption. Multiple lines of evidence implicate gut-derived bacteria and bacterial ligands as a central driver of pathogenesis. Recent developments in culture-independent techniques have facilitated a more accurate description of microbiome composition in cirrhosis and led to the description of measures of dysbiosis shown to be associated with disease. More importantly, metagenomic studies are adding to an understanding of the functional contribution of the microbiota and may prove to be a more clinically relevant biomarker than phylogenetic studies. Much like other dysbiotic states such as inflammatory bowel disease, the microbiota in cirrhosis is characterized by a low microbial and genetic diversity. Therapeutic strategies to diminish this process are currently limited to selective intestinal decontamination with antibiotics. This review summarizes the available data and develops a framework for the use of current and future treatment strategies to diminish the consequences of dysbiosis in cirrhosis. Interventional strategies to bind bacterial products in the gut lumen and blood, and modulate the magnitude of host sensing mechanisms remain an unmet clinical need. A greater understanding of the host-microbiota interaction in cirrhosis is of key importance to inform future interventional strategies to diminish the currently escalating burden of the disease.

Clinical and pathophysiological consequences of alterations in the microbiome in cirrhosis

Cirrhosis is a major cause of mortality worldwide. Exponential rises in prevalence have been observed secondary to increases in obesity and alcohol consumption. Multiple lines of evidence implicate gut-derived bacteria and bacterial ligands as a central driver of pathogenesis. Recent developments in culture-independent techniques have facilitated a more accurate description of microbiome composition in cirrhosis and led to the description of measures of dysbiosis shown to be associated with disease. More importantly, metagenomic studies are adding to an understanding of the functional contribution of the microbiota and may prove to be a more clinically relevant biomarker than phylogenetic studies. Much like other dysbiotic states such as inflammatory bowel disease, the microbiota in cirrhosis is characterized by a low microbial and genetic diversity. Therapeutic strategies to diminish this process are currently limited to selective intestinal decontamination with antibiotics. This review summarizes the available data and develops a framework for the use of current and future treatment strategies to diminish the consequences of dysbiosis in cirrhosis. Interventional strategies to bind bacterial products in the gut lumen and blood, and modulate the magnitude of host sensing mechanisms remain an unmet clinical need. A greater understanding of the host-microbiota interaction in cirrhosis is of key importance to inform future interventional strategies to diminish the currently escalating burden of the disease.

Nitric oxide as a regulator of B. anthracis pathogenicity

Nitric oxide (NO) is a key physiological regulator in eukaryotic and prokaryotic organisms. It can cause a variety of biological effects by reacting with its targets or/and indirectly inducing oxidative stress. NO can also be produced by bacteria including the pathogenic Bacillus anthracis; however, its role in the infectious process only begins to emerge. NO incapacitates macrophages by S-nitrosylating the intracellular proteins and protects B. anthracis from oxidative stress. It is also implicated in the formation of toxic peroxynitrite. In this study we further assessed the effects of B. anthracis NO produced by the NO synthase (bNOS) on bacterial metabolism and host cells in experiments with the bNOS knockout Sterne strain. The mutation abrogated accumulation of nitrite and nitrate as tracer products of NO in the culture medium and markedly attenuated growth in both aerobic and microaerobic conditions. The regulatory role of NO was also suggested by the abnormally high rate of nitrate denitrification by the mutant in the presence of oxygen. Anaerobic regulation mediated by NO was reflected in reduced fermentation of glucose by the mutant correlating with the reduced toxicity of bacteria toward host cells in culture. The toxic effect of NO required permeabilization of the target cells as well as the activity of fermentation-derived metabolite in the conditions of reduced pH. The host cells demonstrated increased phosphorylation of major survivor protein kinase AKT correlating with reduced toxicity of the mutant in comparison with Sterne. Our global proteomic analysis of lymph from the lymph nodes of infected mice harboring bacteria revealed numerous changes in the pattern and levels of proteins associated with the activity of bNOS influencing key cell physiological processes relevant to energy metabolism, growth, signal transduction, stress response, septic shock, and homeostasis. This is the first in vivo observation of the bacterial NO effect on the lymphatic system.