A microbial-derived succinylated bile acid to safeguard liver health.

In this issue of Cell, Nie and co-authors report that the microbe-derived bile acid (BA) 3-succinylated cholic acid protects against the progression of metabolic dysfunction-associated liver disease. Intriguingly, its protective mechanism does not involve traditional BA signaling pathways but is instead linked to the proliferation of the commensal microbe Akkermansia muciniphila.

Gut symbionts alleviate MASH through a secondary bile acid biosynthetic pathway.

The gut microbiota has been found to play an important role in the progression of metabolic dysfunction-associated steatohepatitis (MASH), but the mechanisms have not been established. Here, by developing a click-chemistry-based enrichment strategy, we identified several microbial-derived bile acids, including the previously uncharacterized 3-succinylated cholic acid (3-sucCA), which is negatively correlated with liver damage in patients with liver-tissue-biopsy-proven metabolic dysfunction-associated fatty liver disease (MAFLD). By screening human bacterial isolates, we identified Bacteroides uniformis strains as effective producers of 3-sucCA both in vitro and in vivo. By activity-based protein purification and identification, we identified an enzyme annotated as ß-lactamase in B. uniformis responsible for 3-sucCA biosynthesis. Furthermore, we found that 3-sucCA is a lumen-restricted metabolite and alleviates MASH by promoting the growth of Akkermansia muciniphila. Together, our data offer new insights into the gut microbiota-liver axis that may be leveraged to augment the management of MASH.

Gut Microbiota Orchestrates Energy Homeostasis during Cold.

Microbial functions in the host physiology are a result of the microbiota-host co-evolution. We show that cold exposure leads to marked shift of the microbiota composition, referred to as cold microbiota. Transplantation of the cold microbiota to germ-free mice is sufficient to increase insulin sensitivity of the host and enable tolerance to cold partly by promoting the white fat browning, leading to increased energy expenditure and fat loss. During prolonged cold, however, the body weight loss is attenuated, caused by adaptive mechanisms maximizing caloric uptake and increasing intestinal, villi, and microvilli lengths. This increased absorptive surface is transferable with the cold microbiota, leading to altered intestinal gene expression promoting tissue remodeling and suppression of apoptosis-the effect diminished by co-transplanting the most cold-downregulated strain Akkermansia muciniphila during the cold microbiota transfer. Our results demonstrate the microbiota as a key factor orchestrating the overall energy homeostasis during increased demand.

Dietary fibers affecting gastrointestinal immunity.

Dietary fibers, including chitin, have a major impact on gastrointestinal (GI) physiology and immunity. Two recent articles, by Parrish et al. and Kim et al., credit depletion of dietary fibers or supplementation with chitin, with negative and positive effects, respectively, on the immune system of the murine digestive tract. This has relevant implications for food allergies and systemic metabolism.

Potential roles of gut microbiome and metabolites in modulating ALS in mice.

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disorder, in which the clinical manifestations may be influenced by genetic and unknown environmental factors. Here we show that ALS-prone Sod1 transgenic (Sod1-Tg) mice have a pre-symptomatic, vivarium-dependent dysbiosis and altered metabolite configuration, coupled with an exacerbated disease under germ-free conditions or after treatment with broad-spectrum antibiotics. We correlate eleven distinct commensal bacteria at our vivarium with the severity of ALS in mice, and by their individual supplementation into antibiotic-treated Sod1-Tg mice we demonstrate that Akkermansia muciniphila (AM) ameliorates whereas Ruminococcus torques and Parabacteroides distasonis exacerbate the symptoms of ALS. Furthermore, Sod1-Tg mice that are administered AM are found to accumulate AM-associated nicotinamide in the central nervous system, and systemic supplementation of nicotinamide improves motor symptoms and gene expression patterns in the spinal cord of Sod1-Tg mice. In humans, we identify distinct microbiome and metabolite configurations-including reduced levels of nicotinamide systemically and in the cerebrospinal fluid-in a small preliminary study that compares patients with ALS with household controls. We suggest that environmentally driven microbiome-brain interactions may modulate ALS in mice, and we call for similar investigations in the human form of the disease.

Physiology of γ-aminobutyric acid production by Akkermansia muciniphila.

Gut bacteria hold the potential to produce a broad range of metabolites that can modulate human functions, including molecules with neuroactive potential. One such molecule is γ-aminobutyric acid (GABA), the main inhibitory neurotransmitter of the central nervous system in animals. Metagenomic analyses suggest that the genomes of many gut bacteria encode glutamate decarboxylase (GAD), the enzyme that catalyzes GABA production. The genome of Akkermansia muciniphila, a mucin specialist and potential next-generation probiotic from the human gut, is predicted to encode GAD, suggesting a contributing role in GABA production in the human gut. In this study, A. muciniphila was grown in batch cultures with and without pH control. In both experiments, A. muciniphila was found to produce GABA as a response to acid (pH <5.5), although only when GABA precursors, either glutamate or glutamine, were present in the medium. Proteomic analysis comparing A. muciniphila grown with and without precursors at pH 4 did not show a difference in GAD expression, suggesting that it is expressed regardless of the presence of GABA precursors. To further investigate the function of A. muciniphila GAD, we heterologously expressed the gad gene (encoded by locus tag Amuc_0372) with a His tag in Escherichia coli and purified the GAD protein. Enzyme assays showed GAD activity in a pH range between 4 and 6, with the highest specific activity at pH 5 of 144 ± 16 µM GABA/min/mg. Overall, our results demonstrate the ability of A. muciniphila to produce GABA as an acid response and unravel the conditions under which GABA production in A. muciniphila occurs.IMPORTANCEAkkermansia muciniphila is considered to be a beneficial bacterium from the human gut, but the exact mechanisms by which A. muciniphila influences its host are not yet fully understood. To this end, it is important to identify which metabolites are produced and consumed by A. muciniphila that may contribute to a healthy gut. In the present study, we demonstrate the ability of A. muciniphila to produce γ-aminobutyric acid (GABA) when grown in an acidic environment, which often occurs in the gut. GABA is the major inhibitory neurotransmitter in the central nervous system and is present in the human gut. For this reason, it is considered an important bacterial metabolite. Our finding that A. muciniphila produces GABA in acidic environments adds to the growing body of understanding of its relationship with host health and provides an explanation on how it can survive acid stress in the human gut.

Alternative strategies for the recombinant synthesis, DOPA modification and analysis of mussel foot proteins - A case study for Mefp-3 from Mytilus edulis.

Mussel foot proteins (Mfps) possess unique binding properties to various surfaces due to the presence of L-3,4-dihydroxyphenylalanine (DOPA). Mytilus edulis foot protein-3 (Mefp-3) is one of several proteins in the byssal adhesive plaque. Its localization at the plaque-substrate interface approved that Mefp-3 plays a key role in adhesion. Therefore, the protein is suitable for the development of innovative bio-based binders. However, recombinant Mfp-3s are mainly purified from inclusion bodies under denaturing conditions. Here, we describe a robust and reproducible protocol for obtaining soluble and tag-free Mefp-3 using the SUMO-fusion technology. Additionally, a microbial tyrosinase from Verrucomicrobium spinosum was used for the in vitro hydroxylation of peptide-bound tyrosines in Mefp-3 for the first time. The highly hydroxylated Mefp-3, confirmed by MALDI-TOF-MS, exhibited excellent adhesive properties comparable to a commercial glue. These results demonstrate a concerted and simplified high yield production process for recombinant soluble and tag-free Mfp3-based proteins with on demand DOPA modification.

The role of the probiotic Akkermansia muciniphila in brain functions: insights underpinning therapeutic potential.

The role of Akkermansia muciniphila, one of the most abundant microorganisms of the intestinal microbiota, has been studied extensively in metabolic diseases, such as obesity and diabetes. It is considered a next-generation probiotic microorganism. Although its mechanism of action has not been fully elucidated, accumulating evidence indicates the important role of A. muciniphila in brain functions via the gut-brain axis and its potential as a therapeutic target in various neuropsychiatric disorders. However, only a limited number of studies, particularly clinical studies, have directly assessed the therapeutic effects of A. muciniphila interventions in these disorders. This is the first review to discuss the comprehensive mechanism of A. muciniphila in the gut-brain axis via the protection of the intestinal mucosal barrier and modulation of the immune system and metabolites, such as short-chain fatty acids, amino acids, and amino acid derivatives. Additionally, the role of A. muciniphila and its therapeutic potential in various neuropsychiatric disorders, including Alzheimer's disease and cognitive deficit, amyotrophic lateral sclerosis, Parkinson's disease, and multiple sclerosis, have been discussed. The review suggests the potential role of A. muciniphila in healthy brain functions.

Akkermansia muciniphila plays critical roles in host health.

Akkermansia muciniphila, an intestinal microorganism, belongs to Verrucomicrobia, one of the most abundant microorganisms in the mammalian gut. It is a mucin-degrading bacterium that can colonise intestines of mammals such as humans and mice by utilising mucin as the only nitrogen and carbon source. When A. muciniphila colonises the intestine, its metabolites interact with the intestinal barrier, affecting host health by consolidating the intestinal barrier, regulating metabolic functions of the intestinal and circulatory systems, and regulating immune functions. This review summarised the mechanisms of A. muciniphila-host interactions that are relevant to host health. We focussed on characteristics of A. muciniphila in relation to its metabolites to provide a comprehensive understanding of A. muciniphila and its effects on host health and disease processes.

Akkermansia muciniphila and its membrane protein ameliorates intestinal inflammatory stress and promotes epithelial wound healing via CREBH and miR-143/145.

BACKGROUND: The intestinal epithelial barrier is the interface for interaction between gut microbiota and host metabolic systems. Akkermansia muciniphila (A. muciniphila) is a key player in the colonic microbiota that resides in the mucus layer, whose abundance is selectively decreased in the faecal microbiota of inflammatory bowel disease (IBD) patients. This study aims to investigate the regulatory mechanism among A. muciniphila, a transcription factor cAMP-responsive element-binding protein H (CREBH), and microRNA-143/145 (miR-143/145) in intestinal inflammatory stress, gut barrier integrity and epithelial regeneration. METHODS: A novel mouse model with increased colonization of A muciniphila in the intestine of CREBH knockout mice, an epithelial wound healing assay and several molecular biological techniques were applied in this study. Results were analysed using a homoscedastic 2-tailed t-test. RESULTS: Increased colonization of A. muciniphila in mouse gut enhanced expression of intestinal CREBH, which was associated with the mitigation of intestinal endoplasmic reticulum (ER) stress, gut barrier leakage and blood endotoxemia induced by dextran sulfate sodium (DSS). Genetic depletion of CREBH (CREBH-KO) significantly inhibited the expression of tight junction proteins that are associated with gut barrier integrity, including Claudin5 and Claudin8, but upregulated Claudin2, a tight junction protein that enhances gut permeability, resulting in intestinal hyperpermeability and inflammation. Upregulation of CREBH by A. muciniphila further coupled with miR-143/145 promoted intestinal epithelial cell (IEC) regeneration and wound repair via insulin-like growth factor (IGF) and IGFBP5 signalling. Moreover, the gene expressing an outer membrane protein of A. muciniphila, Amuc_1100, was cloned into a mammalian cell-expression vector and successfully expressed in porcine and human IECs. Expression of Amuc_1100 in IECs could recapitulate the health beneficial effect of A. muciniphila on the gut by activating CREBH, inhibiting ER stress and enhancing the expression of genes involved in gut barrier integrity and IEC's regeneration. CONCLUSIONS: This study uncovers a novel mechanism that links A. muciniphila and its membrane protein with host CREBH, IGF signalling and miRNAs in mitigating intestinal inflammatory stress-gut barrier permeability and promoting intestinal wound healing. This novel finding may lend support to the development of therapeutic approaches for IBD by manipulating the interaction between host genes, gut bacteria and its bioactive components.

Identification and characterisation of a major outer membrane protein from Methylacidiphilum fumariolicum SolV.

The outer membrane (OM) protects Gram-negative bacteria against a hostile environment. The proteins embedded in the OM fulfil a number of tasks that are crucial to the bacterial cell. In this study, we identified and characterised a major outer membrane protein (WP_009059494) from Methylacidiphilum fumariolicum SolV. PRED-TMBB and AlphaFold2 predicted this protein to form a porin with a ß-barrel structure consisting of ten antiparallel ß-sheets and with a small amphipathic N-terminal α-helix in the periplasm. We purified soluble recombinant protein WP_009059494 from E. coli using Tris-HCl buffer with SDS. Antibodies were raised against two peptides in the two large extracellular loops of protein WP_009059494 and immunogold localisation showed this protein to be mainly present in the OM of strain SolV. In addition, this protein is tightly associated with the OM, and is resistant to extraction. Only a small amount can be isolated from the cell envelope using harsh conditions (SDS and boiling). Despite this resistance to extraction, WP_009059494 most likely is an outer membrane protein. A regular lattice could not be detected by negative staining TEM of strain SolV and isolated protein WP_009059494. Considering the specific ecological niche of strain SolV living in a geothermal environment with low pH and high temperatures, this major protein WP_009059494 may act as barrier to resist the extreme conditions found in its natural environment. In addition, we found an absence of the BamB, BamC and BamE proteins of the canonical BAM complex, in Methylacidiphilum and Methylacidimicrobium species. This suggests that these bacteria use a simple BAM complex for folding and transport of OM proteins.

Multiheme hydroxylamine oxidoreductases produce NO during ammonia oxidation in methanotrophs.

Aerobic and nitrite-dependent methanotrophs make a living from oxidizing methane via methanol to carbon dioxide. In addition, these microorganisms cometabolize ammonia due to its structural similarities to methane. The first step in both of these processes is catalyzed by methane monooxygenase, which converts methane or ammonia into methanol or hydroxylamine, respectively. Methanotrophs use methanol for energy conservation, whereas toxic hydroxylamine is a potent inhibitor that needs to be rapidly removed. It is suggested that many methanotrophs encode a hydroxylamine oxidoreductase (mHAO) in their genome to remove hydroxylamine, although biochemical evidence for this is lacking. HAOs also play a crucial role in the metabolism of aerobic and anaerobic ammonia oxidizers by converting hydroxylamine to nitric oxide (NO). Here, we purified an HAO from the thermophilic verrucomicrobial methanotroph Methylacidiphilum fumariolicum SolV and characterized its kinetic properties. This mHAO possesses the characteristic P460 chromophore and is active up to at least 80 °C. It catalyzes the rapid oxidation of hydroxylamine to NO. In methanotrophs, mHAO efficiently removes hydroxylamine, which severely inhibits calcium-dependent, and as we show here, lanthanide-dependent methanol dehydrogenases, which are more prevalent in the environment. Our results indicate that mHAO allows methanotrophs to thrive under high ammonia concentrations in natural and engineered ecosystems, such as those observed in rice paddy fields, landfills, or volcanic mud pots, by preventing the accumulation of inhibitory hydroxylamine. Under oxic conditions, methanotrophs mainly oxidize ammonia to nitrite, whereas in hypoxic and anoxic environments reduction of both ammonia-derived nitrite and NO could lead to nitrous oxide (N2O) production.

Akkermansia muciniphila as a Next-Generation Probiotic in Modulating Human Metabolic Homeostasis and Disease Progression: A Role Mediated by Gut-Liver-Brain Axes?

Appreciation of the importance of Akkermansia muciniphila is growing, and it is becoming increasingly relevant to identify preventive and/or therapeutic solutions targeting gut-liver-brain axes for multiple diseases via Akkermansia muciniphila. In recent years, Akkermansia muciniphila and its components such as outer membrane proteins and extracellular vesicles have been known to ameliorate host metabolic health and intestinal homeostasis. However, the impacts of Akkermansia muciniphila on host health and disease are complex, as both potentially beneficial and adverse effects are mediated by Akkermansia muciniphila and its derivatives, and in some cases, these effects are dependent upon the host physiology microenvironment and the forms, genotypes, and strain sources of Akkermansia muciniphila. Therefore, this review aims to summarize the current knowledge of how Akkermansia muciniphila interacts with the host and influences host metabolic homeostasis and disease progression. Details of Akkermansia muciniphila will be discussed including its biological and genetic characteristics; biological functions including anti-obesity, anti-diabetes, anti-metabolic-syndrome, anti-inflammation, anti-aging, anti-neurodegenerative disease, and anti-cancer therapy functions; and strategies to elevate its abundance. Key events will be referred to in some specific disease states, and this knowledge should facilitate the identification of Akkermansia muciniphila-based probiotic therapy targeting multiple diseases via gut-liver-brain axes.

Nutrient-specific proteomic analysis of the mucin degrading bacterium Akkermansia muciniphila.

Akkermansia muciniphila is a prominent mucin-degrading bacterium that acts as a keystone species in regulating the human gut microbiota. Despite recently increasing research into this bacterium and its relevance to human health, a high-resolution database of its functional proteins remains scarce. Here, we provide a proteomic overview of A. muciniphila grown in different nutrient conditions ranging from defined to complex. Of 2318 protein-coding genes in the genome, we identified 841 (40%) that were expressed at the protein level. Overall, proteins involved in energy production and carbohydrate metabolism indicate that A. muciniphila relies mainly on the Embden-Meyerhof-Parnas pathway, and produces short-chain fatty acids through anaerobic fermentation in a nutrient-specific manner. Moreover, this bacterium possesses a broad repertoire of glycosyl hydrolases, together with putative peptidases and sulfatases, to cleave O-glycosylated mucin. Of them, putative mucin-degrading enzymes (Amuc_1220, Amuc_1120, Amuc_0052, Amuc_0480, and Amuc_0060) are highly abundant in the mucin-supplemented media. Furthermore, A. muciniphila uses mucin-derived monosaccharides as sources of energy and cell wall biogenesis. Our dataset provides nutrient-dependent global proteomes of A. muciniphila ATCC BAA-835 to offer insights into its metabolic functions that shape the composition of the human gut microbiota via mucin degradation.

Genome analysis and 2'-fucosyllactose utilization characteristics of a new Akkermansia muciniphila strain isolated from mice feces.

Akkermansia muciniphila is considered to be a next-generation probiotic, and closely related to host metabolism and immune response. Compared with other probiotics, little is known about its genomic analysis. Therefore, further researches about isolating more A. muciniphila strains and exploring functional genes are needed. In the present study, a new strain isolated from mice feces was identified as A. muciniphila (MucX). Whole-genome sequencing and annotation revealed that MucX possesses key genes necessary for human milk oligosaccharides (HMO) utilization, including α-L-fucosidases, ß-galactosidases, exo-α-sialidases, and ß-acetylhexosaminidases. The complete metabolic pathways for γ-aminobutyric acid and squalene and genes encoding functional proteins, such as the outer membrane protein Amuc_1100, were annotated in the MucX genome. Comparative genome analysis was used to identify functional genes unique to MucX compared to six other A. muciniphila strains. Results showed MucX genome possesses unique genes, including sugar transporters and transferases. Single-strain incubation revealed faster utilization of 2'-fucosyllactose (2'-FL), galacto-oligosaccharides, and lactose by MucX than by A. muciniphila DSM 22959. This study isolated and identified an A. muciniphila strain that can utilize 2'-FL, and expolored the genes related to HMO utilization and special metabolites, which provided a theoretical basis for the further excavation of A. muciniphila function and the compound application with fucosylated oligosaccharides.

Polyphenols as Drivers of a Homeostatic Gut Microecology and Immuno-Metabolic Traits of Akkermansia muciniphila: From Mouse to Man.

Akkermansia muciniphila is a mucosal symbiont considered a gut microbial marker in healthy individuals, as its relative abundance is significantly reduced in subjects with gut inflammation and metabolic disturbances. Dietary polyphenols can distinctly stimulate the relative abundance of A. muciniphila, contributing to the attenuation of several diseases, including obesity, type 2 diabetes, inflammatory bowel diseases, and liver damage. However, mechanistic insight into how polyphenols stimulate A. muciniphila or its activity is limited. This review focuses on dietary interventions in rodents and humans and in vitro studies using different phenolic classes. We provide critical insights with respect to potential mechanisms explaining the effects of polyphenols affecting A. muciniphila. Anthocyanins, flavan-3-ols, flavonols, flavanones, stilbenes, and phenolic acids are shown to increase relative A. muciniphila levels in vivo, whereas lignans exert the opposite effect. Clinical trials show consistent findings, and high intervariability relying on the gut microbiota composition at the baseline and the presence of multiple polyphenol degraders appear to be cardinal determinants in inducing A. muciniphila and associated benefits by polyphenol intake. Polyphenols signal to the AhR receptor and impact the relative abundance of A. muciniphila in a direct and indirect fashion, resulting in the restoration of intestinal epithelial integrity and homeostatic crosstalk with the gut microbiota by affecting IL-22 production. Moreover, recent evidence suggests that A. muciniphila participates in the initial hydrolysis of some polyphenols but does not participate in their complete metabolism. In conclusion, the consumption of polyphenol-rich foods targeting A. muciniphila as a pivotal intermediary represents a promising precision nutritional therapy to prevent and attenuate metabolic and inflammatory diseases.

Increase in Akkermansiaceae in Gut Microbiota of Prostate Cancer-Bearing Mice.

Gut microbiota are reported to be associated with many diseases, including cancers. Several bacterial taxa have been shown to be associated with cancer development or response to treatment. However, longitudinal microbiota alterations during the development of cancers are relatively unexplored. To better understand how microbiota changes, we profiled the gut microbiota composition from prostate cancer-bearing mice and control mice at five different time points. Distinct gut microbiota differences were found between cancer-bearing mice and control mice. Akkermansiaceae was found to be significantly higher in the first three weeks in cancer-bearing mice, which implies its role in the early stage of cancer colonization. We also found that Bifidobacteriaceae and Enterococcaceae were more abundant in the second and last sampling week, respectively. The increments of Akkermansiaceae, Bifidobacteriaceae and Enterococcaceae were previously found to be associated with responses to immunotherapy, which suggests links between these bacteria families and cancers. Additionally, our function analysis showed that the bacterial taxa carrying steroid biosynthesis and butirosin and neomycin biosynthesis were increased, whereas those carrying naphthalene degradation decreased in cancer-bearing mice. Our work identified the bacteria taxa altered during prostate cancer progression and provided a resource of longitudinal microbiota profiles during cancer development in a mouse model.

Pasteurized Akkermansia muciniphila protects from fat mass gain but not from bone loss.

Probiotic bacteria can protect from ovariectomy (ovx)-induced bone loss in mice. Akkermansia muciniphila is considered to have probiotic potential due to its beneficial effect on obesity and insulin resistance. The purpose of the present study was to determine if treatment with pasteurized Akkermansia muciniphila (pAkk) could prevent ovx-induced bone loss. Mice were treated with vehicle or pAkk for 4 wk, starting 3 days before ovx or sham surgery. Treatment with pAkk reduced fat mass accumulation confirming earlier findings. However, treatment with pAkk decreased trabecular and cortical bone mass in femur and vertebra of gonadal intact mice and did not protect from ovx-induced bone loss. Treatment with pAkk increased serum parathyroid hormone (PTH) levels and increased expression of the calcium transporter Trpv5 in kidney suggesting increased reabsorption of calcium in the kidneys. Serum amyloid A 3 (SAA3) can suppress bone formation and mediate the effects of PTH on bone resorption and bone loss in mice and treatment with pAkk increased serum levels of SAA3 and gene expression of Saa3 in colon. Moreover, regulatory T cells can be protective of bone and pAkk-treated mice had decreased number of regulatory T cells in mesenteric lymph nodes and bone marrow. In conclusion, treatment with pAkk protected from ovx-induced fat mass gain but not from bone loss and reduced bone mass in gonadal intact mice. Our findings with pAkk differ from some probiotics that have been shown to protect bone mass, demonstrating that not all prebiotic and probiotic factors have the same effect on bone.

Characterization of sponge-associated Verrucomicrobia: microcompartment-based sugar utilization and enhanced toxin-antitoxin modules as features of host-associated Opitutales.

Bacteria of the phylum Verrucomicrobia are ubiquitous in marine environments and can be found as free-living organisms or as symbionts of eukaryotic hosts. Little is known about host-associated Verrucomicrobia in the marine environment. Here we reconstructed two genomes of symbiotic Verrucomicrobia from bacterial metagenomes derived from the Atlanto-Mediterranean sponge Petrosia ficiformis and three genomes from strains that we isolated from offshore seawater of the Eastern Mediterranean Sea. Phylogenomic analysis of these five strains indicated that they are all members of Verrucomicrobia subdivision 4, order Opitutales. We compared these novel sponge-associated and seawater-isolated genomes to closely related Verrucomicrobia. Genomic analysis revealed that Planctomycetes-Verrucomicrobia microcompartment gene clusters are enriched in the genomes of symbiotic Opitutales including sponge symbionts but not in free-living ones. We hypothesize that in sponge symbionts these microcompartments are used for degradation of l-fucose and l-rhamnose, which are components of algal and bacterial cell walls and therefore may be found at high concentrations in the sponge tissue. Furthermore, we observed an enrichment of toxin-antitoxin modules in symbiotic Opitutales. We suggest that, in sponges, verrucomicrobial symbionts utilize these modules as a defence mechanism against antimicrobial activity deriving from the abundant microbial community co-inhabiting the host.

Methanol Production by "Methylacidiphilum fumariolicum" SolV under Different Growth Conditions.

Industrial methanol production converts methane from natural gas into methanol through a multistep chemical process. Biological methane-to-methanol conversion under moderate conditions and using biogas would be more environmentally friendly. Methanotrophs, bacteria that use methane as an energy source, convert methane into methanol in a single step catalyzed by the enzyme methane monooxygenase, but inhibition of methanol dehydrogenase, which catalyzes the subsequent conversion of methanol into formaldehyde, is a major challenge. In this study, we used the thermoacidophilic methanotroph "Methylacidiphilum fumariolicum" SolV for biological methanol production. This bacterium possesses a XoxF-type methanol dehydrogenase that is dependent on rare earth elements for activity. By using a cultivation medium nearly devoid of lanthanides, we reduced methanol dehydrogenase activity and obtained a continuous methanol-producing microbial culture. The methanol production rate and conversion efficiency were growth-rate dependent. A maximal conversion efficiency of 63% mol methanol produced per mol methane consumed was obtained at a relatively high growth rate, with a methanol production rate of 0.88 mmol/g (dry weight)/h. This study demonstrates that methanotrophs can be used for continuous methanol production. Full-scale application will require additional increases in the titer, production rate, and efficiency, which can be achieved by further decreasing the lanthanide concentration through the use of increased biomass concentrations and novel reactor designs to supply sufficient gases, including methane, oxygen, and hydrogen.IMPORTANCE The production of methanol, an important chemical, is completely dependent on natural gas. The current multistep chemical process uses high temperature and pressure to convert methane in natural gas to methanol. In this study, we used the methanotroph "Methylacidiphilum fumariolicum" SolV to achieve continuous methanol production from methane as the substrate. The production rate was highly dependent on the growth rate of this microorganism, and high conversion efficiencies were obtained. Using microorganisms for the production of methanol might enable the use of more sustainable sources of methane, such as biogas, rather than natural gas.