Age dependent breath methane in the German population

Measurements of methane and nitrous oxide in human breath and the development of UK scale emissions

Exhaled human breath can contain small, elevated concentrations of methane (CH4) and nitrous oxide (N2O), both of which contribute to global warming. These emissions from humans are not well understood and are rarely quantified in global greenhouse gas inventories. This study investigated emissions of CH4 and N2O in human breath from 104 volunteers in the UK population, to better understand what drives these emissions and to quantify national-scale estimates. A total of 328 breath samples were collected, and age, sex, dietary preference, and smoking habits were recorded for every participant. The percentage of methane producers (MPs) identified in this study was 31%. The percentage of MPs was higher in older age groups with 25% of people under the age of 30 classified as MPs compared to 40% in the 30+ age group. Females (38%) were more likely to be MPs than males (25%), though overall concentrations emitted from both MP groups were similar. All participants were found to emit N2O in breath, though none of the factors investigated explained the differences in emissions. Dietary preference was not found to affect CH4 or N2O emissions from breath in this study. We estimate a total emission of 1.04 (0.86-1.40) Gg of CH4 and 0.069 (0.066-0.072) Gg of N2O in human breath annually in the UK, the equivalent of 53.9 (47.8-60.0) Gg of CO2. In terms of magnitude, these values are approximately 0.05% and 0.1% of the total emissions of CH4 and N2O reported in the UK national greenhouse gas inventories.

Radical-Driven Methane Formation in Humans Evidenced by Exogenous Isotope-Labeled DMSO and Methionine

Methane (CH₄), which is produced endogenously in animals and plants, was recently suggested to play a role in cellular physiology, potentially influencing the signaling pathways and regulatory mechanisms involved in nitrosative and oxidative stress responses. In addition, it was proposed that the supplementation of CH₄ to organisms may be beneficial for the treatment of several diseases, including ischemia, reperfusion injury, and inflammation. However, it is still unclear whether and how CH₄ is produced in mammalian cells without the help of microorganisms, and how CH₄ might be involved in physiological processes in humans. In this study, we produced the first evidence of the principle that CH₄ is formed non-microbially in the human body by applying isotopically labeled methylated sulfur compounds, such as dimethyl sulfoxide (DMSO) and methionine, as carbon precursors to confirm cellular CH₄ formation. A volunteer applied isotopically labeled (²H and ¹³C) DMSO on the skin, orally, and to blood samples. The monitoring of stable isotope values of CH₄ convincingly showed the conversion of the methyl groups, as isotopically labeled CH₄ was formed during all experiments. Based on these results, we considered several hypotheses about endogenously formed CH₄ in humans, including physiological aspects and stress responses involving reactive oxygen species (ROS). While further and broader validation studies are needed, the results may unambiguously serve as a proof of concept for the endogenous formation of CH₄ in humans via a radical-driven process. Furthermore, these results might encourage follow-up studies to decipher the potential physiological role of CH₄ and its bioactivity in humans in more detail. Of particular importance is the potential to monitor CH₄ as an oxidative stress biomarker if the observed large variability of CH₄ in breath air is an indicator of physiological stress responses and immune reactions. Finally, the potential role of DMSO as a radical scavenger to counteract oxidative stress caused by ROS might be considered in the health sciences. DMSO has already been investigated for many years, but its potential positive role in medical use remains highly uncertain.

Human metabolic emissions of carbon dioxide and methane and their implications for carbon emissions

Carbon dioxide (CO₂) and methane (CH₄) are important greenhouse gases in the atmosphere and have large impacts on Earth's radiative forcing and climate. Their natural and anthropogenic emissions have often been in focus, while the role of human metabolic emissions has received less attention. In this study, exhaled, dermal and whole-body CO₂ and CH₄ emission rates from a total of 20 volunteers were quantified under various controlled environmental conditions in a climate chamber. The whole-body CO₂ emissions increased with temperature. Individual differences were the most important factor for the whole-body CH₄ emissions. Dermal emissions of CO₂ and CH₄ only contributed ~3.5% and ~5.5% to the whole-body emissions, respectively. Breath measurements conducted on 24 volunteers in a companion study identified one third of the volunteers as CH₄ producers (exhaled CH₄ exceeded 1 ppm above ambient level). The exhaled CH₄ emission rate of these CH₄ producers (4.03 ± 0.71 mg/h/person, mean ± one standard deviation) was ten times higher than that of the rest of the volunteers (non-CH₄ producers; 0.41 ± 0.45 mg/h/person). With increasing global population and the expected large reduction in global anthropogenic carbon emissions in the next decades, metabolic emissions of CH₄ (although not CO₂) from humans may play an increasing role in regional and global carbon budgets.

ROS-driven cellular methane formation: Potential implications for health sciences

Recently it has been proposed that methane might be produced by all living organisms via a mechanism driven by reactive oxygen species that arise through the metabolic activity of cells. Here, we summarise details of this novel reaction pathway and discuss its potential significance for clinical and health sciences. In particular, we highlight the role of oxidative stress in cellular methane formation. As several recent studies also demonstrated the anti-inflammatory potential for exogenous methane-based approaches in mammalians, this article addresses the intriguing question if ROS-driven methane formation has a general physiological role and associated diagnostic potential.

Methane formation driven by reactive oxygen species across all living organisms

Methane (CH₄), the most abundant hydrocarbon in the atmosphere, originates largely from biogenic sources¹ linked to an increasing number of organisms occurring in oxic and anoxic environments. Traditionally, biogenic CH₄ has been regarded as the final product of anoxic decomposition of organic matter by methanogenic archaea. However, plants^2,3, fungi⁴, algae⁵ and cyanobacteria⁶ can produce CH₄ in the presence of oxygen. Although methanogens are known to produce CH₄ enzymatically during anaerobic energy metabolism⁷, the requirements and pathways for CH₄ production by non-methanogenic cells are poorly understood. Here, we demonstrate that CH₄ formation by Bacillus subtilis and Escherichia coli is triggered by free iron and reactive oxygen species (ROS), which are generated by metabolic activity and enhanced by oxidative stress. ROS-induced methyl radicals, which are derived from organic compounds containing sulfur- or nitrogen-bonded methyl groups, are key intermediates that ultimately lead to CH₄ production. We further show CH₄ production by many other model organisms from the Bacteria, Archaea and Eukarya domains, including in several human cell lines. All these organisms respond to inducers of oxidative stress by enhanced CH₄ formation. Our results imply that all living cells probably possess a common mechanism of CH₄ formation that is based on interactions among ROS, iron and methyl donors, opening new perspectives for understanding biochemical CH₄ formation and cycling.

Role of Glucose Breath Test for Small Intestinal Bacterial Overgrowth in Children and Adolescents With Functional Abdominal Pain Disorders in Korea

Background/Aims

Small intestinal bacterial overgrowth (SIBO) is expected in children and adolescents with functional abdominal pain disorders (FAPDs). This study is conducted to estimate the prevalence of SIBO and to investigate the role of SIBO in children and adolescents with FAPDs.

Methods

This prospective study enrolled children with FAPDs fulfilling the Rome IV criteria. A hydrogen-methane glucose breath test was used to diagnose SIBO. A survey of bowel symptoms using questionnaires, birth history, types of feeding, and the presence of allergy was conducted.

Results

Sixty-eight children and adolescents (range, 6-17 years; median, 12.5 years) were enrolled. SIBO was detected in 14 patients (20.6%). Age (≥ 12 years) (P < 0.003) and loose stool (P = 0.048) were significantly more common in children with SIBO than in children without SIBO. However, the history of allergies (P = 0.031) was less common in children with SIBO than those without SIBO. No significant differences were observed in other demographic findings. In multivariate analysis, age (≥ 12 years) was the independent factor predicting SIBO in children with FAPDs.

Conclusions

SIBO is not uncommon in children and adolescents with FAPDs. Among children aged above 12 years and diagnosed with FAPDs, SIBO is a suspected clinical target for treatment to relieve intestinal symptoms. A further study to investigate the association between intestinal bacteria and history of allergy is needed.

Hydrogen and Methane Breath Test in the Diagnosis of Lactose Intolerance

The hydrogen (H₂) breath test is a non-invasive investigation used to diagnose lactose intolerance (LI). Patients with LI may also expire increased amounts of methane (CH₄) during a lactose test. The aim of this study is to evaluate the contribution of CH₄ measurements. We tested 209 children (1–17 years old) with symptoms suggesting LI with lactose H₂ and CH₄ breath tests. The result was positive when the H₂ excretion exceeded 20 parts per million (ppm) and the CH₄ was 10 ppm above the baseline. A clinician, blinded for the results of the breath test, registered the symptoms. Of the patient population, 101/209 (48%) were negative for both H₂ and CH₄; 96/209 (46%) had a positive H₂ breath test result; 31/96 (32%) were also positive for CH₄; 12/209 (6%) patients were only positive for CH₄. The majority of hydrogen producers showed symptoms, whereas this was only the case in half of the H₂-negative CH₄ producers. Almost all patients treated with a lactose-poor diet reported significant symptom improvement. These results indicate that CH₄ measurements may possibly be of additional value for the diagnosis of LI, since 5.7% of patients were negative for H₂ and positive for CH₄, and half of them experienced symptoms during the test.

Machine Learning-Reinforced Noninvasive Biosensors for Healthcare

The emergence and development of noninvasive biosensors largely facilitate the collection of physiological signals and the processing of health-related data. The utilization of appropriate machine learning algorithms improves the accuracy and efficiency of biosensors. Machine learning-reinforced biosensors are started to use in clinical practice, health monitoring, and food safety, bringing a digital revolution in healthcare. Herein, the recent advances in machine learning-reinforced noninvasive biosensors applied in healthcare are summarized. First, different types of noninvasive biosensors and physiological signals collected are categorized and summarized. Then machine learning algorithms adopted in subsequent data processing are introduced and their practical applications in biosensors are reviewed. Finally, the challenges faced by machine learning-reinforced biosensors are raised, including data privacy and adaptive learning capability, and their prospects in real-time monitoring, out-of-clinic diagnosis, and onsite food safety detection are proposed.

Fructose Malabsorption in Chilean Children Undergoing Fructose Breath Test at a Tertiary Hospital

Fructose is a highly abundant carbohydrate in western diet and may induce bowel symptoms in children as in adults. The main objective of this study is to describe the frequency of fructose malabsorption (FM) in symptomatic patients 18 years or younger undergoing fructose breath test in a single tertiary center between 2013 and 2018, and to evaluate whether certain symptoms are related to positivity of the test. Out of 273 tests 183 (67%) were compatible with FM. The most frequent pretest symptom in the overall study population was bloating (83%), followed by abdominal pain (73%). Patients with positive test were younger than those with a negative test (median 5 vs 8 years, P < 0.001). In multivariate analysis, which included age, sex, and symptoms (diarrhea, abdominal pain, bloating, nausea), only age <6 years (odds ratio 2.93, 95% confidence interval 1.64-5.23) and absence of nausea (odds ratio = 3.32, 95% confidence interval 1.56-7.05) were associated with FM.

Comparing the rates of methane production in patients with and without appendectomy: results from a large-scale cohort

There is no clear study identifying the microbiome of the appendix. However, in other diverticular conditions, such as diverticulosis, methanogens appear important. We investigated whether patients who had undergone appendectomies had decreased levels of exhaled methane (CH₄). Consecutive patients who underwent breath testing (BT) from November 2005 to October 2013 were deterministically linked to electronic health records. The numbers of patients with CH₄ ≥ 1 ppm (detectable) and ≥ 3 and ≥ 10 ppm (excess) were compared between patients who did and did not undergo appendectomy using a multivariable model adjusted for age and sex. Of the 4977 included patients (48.0 ± 18.4 years, 30.1% male), 1303 (26.2%) had CH₄ ≥ 10 ppm, and 193 (3.9%) had undergone appendectomy. Appendectomy was associated with decreased odds of CH₄ ≥ 1, ≥ 3, and ≥ 10 ppm (ORs (95% CI) = 0.67 (0.47–0.93), p = 0.02; 0.65 (0.46–0.92), p = 0.01; and 0.66 (0.46–0.93), p = 0.02, respectively). Additionally, the percentage of CH₄ producers increased 4-fold from the first to ninth decade of life. This is the first study to report that appendectomy is associated with decreased exhaled CH₄. The appendix may play an active physiologic role as a reservoir of methanogens.

The Unexplored World of Human Virome, Mycobiome, and Archaeome in Aging

In the last decades, improvements in different aspects of sanitation, medical care, and nutrition, among others, have permitted an increase in the average lifespan of human population around the world. These advances have stimulated an increased interest in the study of the aging process and age-sensitive characteristics, such as the microbial community that colonizes the human body (microbiome). The human microbiome is composed of bacteria (bacteriome), archaea (archaeome), fungi (mycobiome), and viruses (virome). To date, research has mainly been centered on the composition of the bacteriome, with other members remain poorly studied. Interestingly, changes in the composition of the microbiome have been implicated in aging and age-related diseases. Therefore, in the present perspective, we suggest expanding the scope to research to include the role and the possible associations that the other members of the microbiome could have in the aging organism. An expanded view of the microbiome would increase our knowledge of the physiology of aging and may be particularly valuable for the treatment and diagnosis of age-related diseases.

Methane Production and Bioactivity-A Link to Oxido-Reductive Stress

Biological methane formation is associated with anoxic environments and the activity of anaerobic prokaryotes (Archaea). However, recent studies have confirmed methane release from eukaryotes, including plants, fungi, and animals, even in the absence of microbes and in the presence of oxygen. Furthermore, it was found that aerobic methane emission in plants is stimulated by a variety of environmental stress factors, leading to reactive oxygen species (ROS) generation. Further research presented evidence that molecules with sulfur and nitrogen bonded methyl groups such as methionine or choline are carbon precursors of aerobic methane formation. Once generated, methane is widely considered to be physiologically inert in eukaryotes, but several studies have found association between mammalian methanogenesis and gastrointestinal (GI) motility changes. In addition, a number of recent reports demonstrated anti-inflammatory potential for exogenous methane-based approaches in model anoxia-reoxygenation experiments. It has also been convincingly demonstrated that methane can influence the downstream effectors of transiently increased ROS levels, including mitochondria-related pro-apoptotic pathways during ischemia-reperfusion (IR) conditions. Besides, exogenous methane can modify the outcome of gasotransmitter-mediated events in plants, and it appears that similar mechanism might be active in mammals as well. This review summarizes the relevant literature on methane-producing processes in eukaryotes, and the available results that underscore its bioactivity. The current evidences suggest that methane liberation and biological effectiveness are both linked to cellular redox regulation. The data collectively imply that exogenous methane influences the regulatory mechanisms and signaling pathways involved in oxidative and nitrosative stress responses, which suggests a modulator role for methane in hypoxia-linked pathologies.

Long-term monitoring of breath methane

In recent years, methane as a component of exhaled human breath has been considered as a potential bioindicator providing information on microbial activity in the intestinal tract. Several studies indicated a relationship between breath methane status and specific gastrointestinal disease. So far, almost no attention has been given to the temporal variability of breath methane production by individual persons. Thus here, for the first time, long-term monitoring was carried out measuring breath methane of three volunteers over periods between 196 and 1002days. Results were evaluated taking into consideration the health status and specific medical intervention events for each individual during the monitoring period, and included a gastroscopy procedure, a vaccination, a dietary change, and chelate therapy. As a major outcome, breath methane mixing ratios show considerable variability within a person-specific range of values. Interestingly, decreased breath methane production often coincided with gastrointestinal complaints whereas influenza infections were mostly accompanied by increased breath methane production. A gastroscopic examination as well as a change to a low-fructose diet led to a dramatic shift of methane mixing ratios from high to low methane production. In contrast, a typhus vaccination as well as single chelate injections resulted in significant short-term methane peaks. Thus, this study clearly shows that humans can change from high to low methane emitters and vice versa within relatively short time periods. In the case of low to medium methane emitters the increase observed in methane mixing ratios, likely resulting from immune reactions and inflammatory processes, might indicate non-microbial methane formation under aerobic conditions. Although detailed reaction pathways are not yet known, aerobic methane formation might be related to cellular oxidative-reductive stress reactions. However, a detailed understanding of the pathways involved in human methane formation is necessary to enable comprehensive interpretation of methane breath levels.

Human age and skin physiology shape diversity and abundance of Archaea on skin

The human skin microbiome acts as an important barrier protecting our body from pathogens and other environmental influences. Recent investigations have provided evidence that Archaea are a constant but highly variable component of the human skin microbiome, yet factors that determine their abundance changes are unknown. Here, we tested the hypothesis that the abundance of archaea on human skin is influenced by human age and skin physiology by quantitative PCR of 51 different skin samples taken from human subjects of various age. Our results reveal that archaea are more abundant in human subjects either older than 60 years or younger than 12 years as compared to middle-aged human subjects. These results, together with results obtained from spectroscopy analysis, allowed us gain first insights into a potential link of lower sebum levels and lipid content and thus reduced skin moisture with an increase in archaeal signatures. Amplicon sequencing of selected samples revealed the prevalence of specific eury- and mainly thaumarchaeal taxa, represented by a core archaeome of the human skin.

Genomics and metagenomics of trimethylamine-utilizing Archaea in the human gut microbiome

The biological significance of Archaea in the human gut microbiota is largely unclear. We recently reported genomic and biochemical analyses of the Methanomassiliicoccales, a novel order of methanogenic Archaea dwelling in soil and the animal digestive tract. We now show that these Methanomassiliicoccales are present in published microbiome data sets from eight countries. They are represented by five Operational Taxonomic Units present in at least four cohorts and phylogenetically distributed into two clades. Genes for utilizing trimethylamine (TMA), a bacterial precursor to an atherosclerogenic human metabolite, were present in four of the six novel Methanomassiliicoccales genomes assembled from ELDERMET metagenomes. In addition to increased microbiota TMA production capacity in long-term residential care subjects, abundance of TMA-utilizing Methanomassiliicoccales correlated positively with bacterial gene count for TMA production and negatively with fecal TMA concentrations. The two large Methanomassiliicoccales clades have opposite correlations with host health status in the ELDERMET cohort and putative distinct genomic signatures for gut adaptation.

Diagnosing lactose malabsorption in children: difficulties in interpreting hydrogen breath test results

Lactose malabsorption (LM) is caused by insufficient enzymatic degradation of the disaccharide by intestinal lactase. Although hydrogen (H2) breath tests (HBTs) are routinely applied to diagnose LM, false-negative results are not uncommon. Thirty-two pediatric patients (19 females, 13 males) were included in this prospective study. After oral lactose administration (1 g kg(-1) bodyweight to a maximum of 25 g), breath H2 was measured by electrochemical detection. HBT was considered positive if H2 concentration exceeded an increase of  ⩾20 ppm from baseline. In addition to H2, exhaled methane (CH4), blood glucose concentrations and clinical symptoms (flatulence, abdominal pain, diarrhea) were monitored. A positive HBT indicating LM was found in 12/32 (37.5%) patients. Only five (41.7%, 5/12) of these had clinical symptoms during HBT indicating lactose intolerance (LI). Decreased blood glucose concentration increments (⩽20 mg dL(-1) (⩽1.1 mmol L(-1))) were found in 3/5 of these patients. CH4 concentrations  ⩾10 ppm at any time during the test were observed in 5/32 (15.6%) patients and in 9/32 (28.1%) between 1 ppm and 9 ppm above baseline after lactose ingestion. In patients with positive HBT 10/12 (83.3%) showed elevated CH4 (>1 ppm) above baseline in breath gas, whereas in patients with negative HBT this figure was only 4/17 (23.5%). In addition to determining H2 in exhaled air, documentation of clinical symptoms, measurement of blood glucose and breath CH4 concentrations may be helpful in deciding whether in a given case an HBT correctly identifies patients with clinically relevant LM.

Modeling of breath methane concentration profiles during exercise on an ergometer

We develop a simple three compartment model based on mass balance equations which quantitatively describes the dynamics of breath methane concentration profiles during exercise on an ergometer. With the help of this model it is possible to estimate the endogenous production rate of methane in the large intestine by measuring breath gas concentrations of methane.

Stable isotope and high precision concentration measurements confirm that all humans produce and exhale methane

Mammalian formation of methane (methanogenesis) is widely considered to occur exclusively by anaerobic microbial activity in the gastrointestinal tract. Approximately one third of humans, depending on colonization of the gut by methanogenic archaea, are considered methane producers based on the classification terminology of high and low emitters. In this study laser absorption spectroscopy was used to precisely measure concentrations and stable carbon isotope signatures of exhaled methane in breath samples from 112 volunteers with an age range from 1 to 80 years. Here we provide analytical evidence that volunteers exhaled methane levels were significantly above background (inhaled) air. Furthermore, stable carbon isotope values of the exhaled methane unambiguously confirmed that this gas was produced by all of the human subjects studied. Based on the emission and stable carbon isotope patterns of various age groups we hypothesize that next to microbial sources in the gastrointestinal tracts there might be other, as yet unidentified, processes involved in methane formation supporting the idea that humans might also produce methane endogenously in cells. Finally we suggest that stable isotope measurements of volatile organic compounds such as methane might become a useful tool in future medical research diagnostic programs.

Exhaled methane concentration profiles during exercise on an ergometer

Exhaled methane concentration measurements are extensively used in medical investigation of certain gastrointestinal conditions. However, the dynamics of endogenous methane release is largely unknown. Breath methane profiles during ergometer tests were measured by means of a photoacoustic spectroscopy based sensor. Five methane-producing volunteers (with exhaled methane level being at least 1 ppm higher than room air) were measured. The experimental protocol consisted of 5 min rest--15 min pedalling (at a workload of 75 W)--5 min rest. In addition, hemodynamic and respiratory parameters were determined and compared to the estimated alveolar methane concentration. The alveolar breath methane level decreased considerably, by a factor of 3-4 within 1.5 min, while the estimated ventilation-perfusion ratio increased by a factor of 2-3. Mean pre-exercise and exercise methane concentrations were 11.4 ppm (SD:7.3) and 2.8 ppm (SD:1.9), respectively. The changes can be described by the high sensitivity of exhaled methane to ventilation-perfusion ratio and are in line with the Farhi equation.

Review article: breath analysis in inflammatory bowel diseases

BACKGROUND

There is an urgent need for cheap, reproducible, easy to perform and specific biomarkers for diagnosis, differentiation and stratification of inflammatory bowel disease (IBD) patients. Technical advances allow for the determination of volatile organic compounds in the human breath to differentiate between health and disease.

AIM

Review and discuss medical literature on volatile organic compounds in exhaled human breath in GI disorders, focusing on diagnosis and differentiation of IBD.

METHODS

A systematic search in PubMed, Ovid Medline and Scopus was completed using appropriate keywords. In addition, a bibliography search of each article was performed.

RESULTS

Mean breath pentane, ethane, propane, 1-octene, 3-methylhexane, 1-decene and NO levels were elevated (P < 0.05 to P < 10(-7)) and mean breath 1-nonene, (E)-2-nonene, hydrogen sulphide and methane were decreased in IBD compared to healthy controls (P = 0.003 to P < 0.001). A combined panel of 3 volatile organic compounds (octene, (E)-2-nonene and decene) showed the best discrimination between paediatric IBD and controls (AUC 0.96). Breath condensate cytokines were higher in IBD compared to healthy individuals (P < 0.008). Breath pentane, ethane, propane, isoprene and NO levels correlated with disease activity in IBD patients. Breath condensate interleukin-1β showed an inverse relation with clinical disease activity.

CONCLUSIONS

Breath analysis in IBD is a promising approach that is not yet ready for routine clinical use, but data from other gastrointestinal diseases suggest the feasibility for use of this technology in clinical practice. Well-designed future trials, incorporating the latest breath detection techniques, need to determine the exact breath metabolome pattern linked to diagnosis and phenotype of IBD.

Archaea and the human gut: New beginning of an old story

Methanogenic archaea are known as human gut inhabitants since more than 30 years ago through the detection of methane in the breath and isolation of two methanogenic species belonging to the order Methanobacteriales, Methanobrevibacter smithii and Methanosphaera stadtmanae. During the last decade, diversity of archaea encountered in the human gastrointestinal tract (GIT) has been extended by sequence identification and culturing of new strains. Here we provide an updated census of the archaeal diversity associated with the human GIT and their possible role in the gut physiology and health. We particularly focus on the still poorly characterized 7^th order of methanogens, the Methanomassiliicoccales, associated to aged population. While also largely distributed in non-GIT environments, our actual knowledge on this novel order of methanogens has been mainly revealed through GIT inhabitants. They enlarge the number of final electron acceptors of the gut metabolites to mono- di- and trimethylamine. Trimethylamine is exclusively a microbiota-derived product of nutrients (lecithin, choline, TMAO, L-carnitine) from normal diet, from which seems originate two diseases, trimethylaminuria (or Fish-Odor Syndrome) and cardiovascular disease through the proatherogenic property of its oxidized liver-derived form. This therefore supports interest on these methanogenic species and its use as archaebiotics, a term coined from the notion of archaea-derived probiotics.