Identification and Characterization of a Novel Species of Genus Akkermansia with Metabolic Health Effects in a Diet-Induced Obesity Mouse Model

Cross-talk between the gut microbiota and hypothyroidism: a bidirectional two-sample Mendelian randomization study

Background

Multiple observational studies suggest a connection between the composition of the gut microbiota and hypothyroidism. However, it has yet to be determined whether the gut microbiota has a causal effect on hypothyroidism.

Methods

To investigate the connection between the gut microbiota and hypothyroidism, two-sample Mendelian randomization was performed using data from a genome-wide association study meta-analysis (n = 18,430) conducted by the MiBioGen consortium. Summary statistics for hypothyroidism (26,342 cases and 59,827 controls) were obtained using the data from the FinnGen consortium R8 release data. To investigate the causal link between the gut microbiota and hypothyroidism, various methods, including MR-Egger, weighted median, weighted model, simple model, MR-PRESSO, and inverse variance weighted (IVW), were employed. The bacteria that were causally linked to hypothyroidism in forward Mendelian randomization analysis were subjected to reverse Mendelian randomization analysis. Cochran's Q statistics were utilized to gauge the heterogeneity of the instrumental variables.

Results

The results indicated that Akkermansia had a positive impact on hypothyroidism, with an odds ratio of 0.84 (95% CI 0.74-0.95, p = 0.01) based on the inverse variance-weighted estimates. Additionally, Anaerostipes (OR = 1.17, 95% CI 1.01-1.36, p = 0.04), Butyrivibrio (OR = 0.93, 95% CI 0.88-0.99, p = 0.02), Holdemania (OR = 0.89, 95% CI 0.81-0.99, p = 0.03), Intestinimonas (OR = 1.13, 95% CI 1.02-1.26, p = 0.03), Ruminiclostridium5 (OR = 1.19, 95% CI 1.01-1.41, p = 0.04), and Ruminococcaceae UCG-011 (OR = 0.91, 95% CI 0.84-0.99, p = 0.03) were identified. The gut microbiota was not significantly affected by hypothyroidism, as indicated by the results of the reverse MR analysis. There was no significant variation in the instrumental variables or horizontal pleiotropy.

Conclusion

The findings of this study using two-sample Mendelian randomization indicate a causal relationship between Akkermansia and hypothyroidism. Increased Akkermansia inhibits the onset and progression of hypothyroidism. Additional randomized controlled experiments are necessary to elucidate the beneficial impact of probiotics on hypothyroidism and their distinct protective mechanisms.

Neuroprotection by agmatine: Possible involvement of the gut microbiome?

Agmatine, an endogenous polyamine derived from L-arginine, elicits tremendous multimodal neuromodulant properties. Alterations in agmatinergic signalling are closely linked to the pathogeneses of several brain disorders. Importantly, exogenous agmatine has been shown to act as a potent neuroprotectant in varied pathologies, including brain ageing and associated comorbidities. The antioxidant, anxiolytic, analgesic, antidepressant and memory-enhancing activities of agmatine may derive from its ability to regulate several cellular pathways; including cell metabolism, survival and differentiation, nitric oxide signalling, protein translation, oxidative homeostasis and neurotransmitter signalling. This review briefly discusses mammalian metabolism of agmatine and then proceeds to summarize our current understanding of neuromodulation and neuroprotection mediated by agmatine. Further, the emerging exciting bidirectional links between agmatine and the resident gut microbiome and their implications for brain pathophysiology and ageing are also discussed.

Potential effects of Ag ion on the host by changing the structure of its gut microbiota

Silver (Ag) can change the structure of the gut microbiota (GM), but how such change may affect host health is unknown. In this study, mice were exposed to silver acetate daily for 120 days. During this period, Ag accumulation in the liver was measured, its effects on GM structure were analyzed, and potential metabolic changes in liver and serum were examined. Although Ag accumulation remained unchanged in most treatments, the ratio of Firmicutes to Bacteroidetes at the phylum level increased and changes in the relative abundance of 33 genera were detected, suggesting that Ag altered the energy metabolism of mice via changes in the gut GM. In serum and liver, 34 and 72 differentially expressed metabolites were identified, respectively. The KEGG pathways thus enriched mainly included those involving the metabolism of amino acids, organic acids, lipids, and purine. Strong correlations were found between 33 % of the microorganisms with altered relative abundances and 46 % of the differentially expressed metabolites. The resulting clusters yielded two communities responsible for host inflammation and energy metabolism. Overall, these results demonstrate potential effects of Ag on the host, by changing its GM structure, and the need to consider them when evaluating the health risk of Ag.

Reclassification of eight Akkermansia muciniphila strains and description of Akkermansia massiliensis sp. nov. and Candidatus Akkermansia timonensis, isolated from human feces

Akkermansia muciniphila is a human intestinal tract bacterium that plays an important role in the mucus layer renewal. Several studies have demonstrated that it is a modulator for gut homeostasis and a probiotic for human health. The Akkermansia genus contains two species with standing in nomenclature but their genomic diversity remains unclear. In this study, eight new Akkermansia sp. strains were isolated from the human gut. Using the digital DNA-DNA hybridization (dDDH), average nucleotide identity (ANI) and core genome-based phylogenetic analysis applied to 104 A. muciniphila whole genomes sequences, strains were reclassified into three clusters. Cluster I groups A. muciniphila strains (including strain ATCC BAA-835^T as type strain), whereas clusters II and III represent two new species. A member of cluster II, strain Marseille-P6666 differed from A. muciniphila strain ATCC BAA-835^T and from A. glycaniphila strain Pyt^T in its ability to grow in microaerophilic atmosphere up to 42 °C, to assimilate various carbon sources and to produce acids from a several compounds. The major fatty acids of strain Marseille-P6666 were 12-methyl-tetradecanoic and pentadecanoic acids. The DNA G + C content of strain Marseille-P6666 was 57.8%. On the basis of these properties, we propose the name A. massiliensis sp. nov. for members of cluster II, with strain Marseille-P6666^T (= CSUR P6666 = CECT 30548) as type strain. We also propose the name "Candidatus Akkermansia timonensis" sp. nov. for the members of cluster III, which contains only uncultivated strains, strain Akk0196 being the type strain.

Novel Candidate Microorganisms for Fermentation Technology: From Potential Benefits to Safety Issues

Fermentation is one of the oldest known production processes and the most technologically valuable in terms of the food industry. In recent years, increasing nutrition and health awareness has also changed what is expected from fermentation technology, and the production of healthier foods has started to come a little more forward rather than increasing the shelf life and organoleptic properties of foods. Therefore, in addition to traditional microorganisms, a new generation of (novel) microorganisms has been discovered and research has shifted to this point. Novel microorganisms are known as either newly isolated genera and species from natural sources or bacterial strains derived from existing bacteria. Although novel microorganisms are mostly studied for their use in novel food production in terms of gut-microbiota modulation, recent innovative food research highlights their fermentative effects and usability, especially in food modifications. Herein, Clostridium butyricum, Bacteroides xylanisolvens, Akkermansia muciniphila, Mycobacterium setense manresensis, and Fructophilic lactic acid bacteria (FLAB) can play key roles in future candidate microorganisms for fermentation technology in foods. However, there is also some confusion about the safety issues related to the use of these novel microorganisms. This review paper focuses on certain novel candidate microorganisms for fermentation technology with a deep view of their functions, benefits, and safety issues.