A thousand metagenome-assembled genomes of Akkermansia reveal phylogroups and geographical and functional variations in the human gut

Akkermansia muciniphila: biology, microbial ecology, host interactions and therapeutic potential

Akkermansia muciniphila is a gut bacterium that colonizes the gut mucosa, has a role in maintaining gut health and shows promise for potential therapeutic applications. The discovery of A. muciniphila as an important member of our gut microbiome, occupying an extraordinary niche in the human gut, has led to new hypotheses on gut health, beneficial microorganisms and host-microbiota interactions. This microorganism has established a unique position in human microbiome research, similar to its role in the gut ecosystem. Its unique traits in using mucin sugars and mechanisms of action that can modify host health have made A. muciniphila a subject of enormous attention from multiple research fields. A. muciniphila is becoming a model organism studied for its ability to modulate human health and gut microbiome structure, leading to commercial products, a genetic model and possible probiotic formulations. This Review provides an overview of A. muciniphila and Akkermansia genus phylogeny, ecophysiology and diversity. Furthermore, the Review discusses perspectives on ecology, strategies for harnessing beneficial effects of A. muciniphila for human mucosal metabolic and gut health, and its potential as a biomarker for diagnostics and prognostics.

Protocol for the construction and functional profiling of metagenome-assembled genomes for microbiome analyses

Constructing metagenome-assembled genomes (MAGs) from complex metagenomic samples involves a series of bioinformatics operations, each requiring deep bioinformatics knowledge. Here, we present a protocol for constructing MAGs and conducting functional profiling to address biological questions. We describe steps for system configuration, data downloads, read processing, removal of human DNA contamination, metagenomic assembly, and statistical quality assessment of the final assembly. Additionally, we detail procedures for the construction and refinement of MAGs, as well as the functional profiling of MAGs.

Pangenomic analysis identifies correlations between Akkermansia species and subspecies and human health outcomes

Aim: Akkermansia are common members of the human gastrointestinal microbiota. The prevalence of these mucophilic bacteria, especially Akkermansia muciniphila (A. muciniphila), correlates with immunological and metabolic health. The genus Akkermansia in humans includes species with significantly larger genomes than A. muciniphila, leading us to postulate that this added genetic content may influence how they impact human metabolic and immunological health. Methods: We conducted a pangenomic analysis of 234 Akkermansia complete or near-complete genomes. We also used high-resolution species and subspecies assignments to reanalyze publicly available metagenomic datasets to determine if there are relationships between Akkermansia species and A. muciniphila clades with various disease outcomes. Results: Analysis of genome-wide average nucleotide identity, 16S rRNA gene identity, conservation of core Akkermansia genes, and analysis of the fatty acid composition of representative isolates support the partitioning of the genus Akkermansia into several species. In addition, A. muciniphila sensu stricto, the most prevalent Akkermansia species in humans, should be subdivided into two subspecies. For a pediatric cohort, we observed species-specific correlations between Akkermansia abundance with baseline obesity or after various interventions. For inflammatory bowel disease cohorts, we identified a decreased abundance of Akkermansia in patients with ulcerative colitis or Crohn's disease, which was species and subspecies-dependent. In patients undergoing immune checkpoint inhibitor therapies for non-small cell lung carcinoma, we observed a significant association between one A. muciniphila subspecies and survival outcomes. Conclusion: Our findings suggest that the prevalence of specific Akkermansia species and/or subspecies can be crucial in evaluating their association with human health, particularly in different disease contexts, and is an important consideration for their use as probiotics.

Function and therapeutic prospects of next-generation probiotic Akkermansia muciniphila in infectious diseases

Akkermansia muciniphila is a gram-negative bacterium that colonizes the human gut, making up 3-5% of the human microbiome. A. muciniphila is a promising next-generation probiotic with clinical application prospects. Emerging studies have reported various beneficial effects of A. muciniphila including anti-cancer, delaying aging, reducing inflammation, improving immune function, regulating nervous system function, whereas knowledge on its roles and mechanism in infectious disease is currently unclear. In this review, we summarized the basic characteristics, genome and phenotype diversity, the influence of A. muciniphila and its derived components on infectious diseases, such as sepsis, virus infection, enteric infection, periodontitis and foodborne pathogen induced infections. We also provided updates on mechanisms how A. muciniphila protects intestinal barrier integrity and modulate host immune response. In summary, we believe that A. muciniphila is a promising therapeutic probiotic that may be applied for the treatment of a variety of infectious diseases.

Insights into early evolutionary adaptations of the Akkermansia genus to the vertebrate gut

Akkermansia, a relevant mucin degrader from the vertebrate gut microbiota, is a member of the deeply branched Verrucomicrobiota, as well as the only known member of this phylum to be described as inhabitants of the gut. Only a few Akkermansia species have been officially described so far, although there is genomic evidence addressing the existence of more species-level variants for this genus. This niche specialization makes Akkermansia an interesting model for studying the evolution of microorganisms to their adaptation to the gastrointestinal tract environment, including which kind of functions were gained when the Akkermansia genus originated or how the evolutionary pressure functions over those genes. In order to gain more insight into Akkermansia adaptations to the gastrointestinal tract niche, we performed a phylogenomic analysis of 367 high-quality Akkermansia isolates and metagenome-assembled genomes, in addition to other members of Verrucomicrobiota. This work was focused on three aspects: the definition of Akkermansia genomic species clusters and the calculation and functional characterization of the pangenome for the most represented species; the evolutionary relationship between Akkermansia and their closest relatives from Verrucomicrobiota, defining the gene families which were gained or lost during the emergence of the last Akkermansia common ancestor (LAkkCA) and; the evaluation of the evolutionary pressure metrics for each relevant gene family of main Akkermansia species. This analysis found 25 Akkermansia genomic species clusters distributed in two main clades, divergent from their non-Akkermansia relatives. Pangenome analyses suggest that Akkermansia species have open pangenomes, and the gene gain/loss model indicates that genes associated with mucin degradation (both glycoside hydrolases and peptidases), (micro)aerobic metabolism, surface interaction, and adhesion were part of LAkkCA. Specifically, mucin degradation is a very ancestral innovation involved in the origin of Akkermansia. Horizontal gene transfer detection suggests that Akkermansia could receive genes mostly from unknown sources or from other Gram-negative gut bacteria. Evolutionary metrics suggest that Akkemansia species evolved differently, and even some conserved genes suffered different evolutionary pressures among clades. These results suggest a complex evolutionary landscape of the genus and indicate that mucin degradation could be an essential feature in Akkermansia evolution as a symbiotic species.

Function of Akkermansia muciniphila in type 2 diabetes and related diseases

The prevalence of type 2 diabetes (T2D) is increasing worldwide, with many patients developing long-term complications that affect their cardiovascular, urinary, alimentary, and other systems. A growing body of literature has reported the crucial role of gut microbiota in metabolic diseases, one of which, Akkermansia muciniphila, is considered the "next-generation probiotic" for alleviating metabolic disorders and the inflammatory response. Although extensive research has been conducted on A. muciniphila, none has summarized its regulation in T2D. Hence, this review provides an overview of the effects and multifaceted mechanisms of A. muciniphila on T2D and related diseases, including improving metabolism, alleviating inflammation, enhancing intestinal barrier function, and maintaining microbiota homeostasis. Furthermore, this review summarizes dietary strategies for increasing intestinal A. muciniphila abundance and effective gastrointestinal delivery.

Dysbiosis and reduced small intestinal function are required to induce intestinal insufficiency in mice

Extensive bowel resection can lead to short bowel syndrome and intestinal failure. Resection-induced dysbiosis may be related to the specific anatomic site of resection and influences the disease progression. Although patients with end-jejunostomy are at high risk for intestinal failure, preservation of the ileocecal valve and colon counteracts this risk. The present study investigated the role of the cecum in maintaining microbial homeostasis after different types of small bowel resection. Male C57BL6/J mice were anesthetized by intraperitoneal injection of ketamine-xylazine and received extended ileocecal resection (extended ICR), limited ileocecal resection (limited ICR), or mid-small bowel resection (SBR). Stool samples were collected before surgery and between postoperative days 2-7, for 16S rRNA gene sequencing. Only extended ICR, but neither limited ICR nor SBR, induced intestinal insufficiency. α-Diversity was reduced in both ICR variants but not after SBR. All resections resulted in an increase in Proteobacteria. Pathobionts, such as Clostridia, Shigella, and Enterococcus, increased after SBR while Muribaculaceae, Lactobacillus, and Lachnospiraceae decreased. Limited ICR resulted in an increase of members of the Clostridium sensu stricto group, Terrisporobacter and Enterococcus and a decrease of Muribaculaceae. The increase of Enterococcus was even more pronounced after extended ICR while Muribaculaceae and Akkermansia were dramatically reduced. Both ICR variants caused a decrease in steroid biosynthesis and glycosaminoglycan degradation-associated pathways, suggesting altered bile acid transformation and mucus utilization.NEW & NOTEWORTHY Resection-induced dysbiosis affects disease progression in patients with short bowel syndrome. Severe dysbiosis occurs after removal of the ileocecal valve, even in the absence of short bowel conditions, and is associated with the loss of Muribaculaceae and Akkermansia and an increase of Clostridium and Enterococcus. The preservation of the cecum should be considered in surgical therapy, and dysbiosis should be targeted based on its specific anatomical signature to improve postoperative bacterial colonization.

Rational consideration of Akkermansia muciniphila targeting intestinal health: advantages and challenges

As one of the promising next-generation probiotics (NGPs), Akkermansia muciniphila, a well-known mucin-degrading bacterium, has been proven to be closely related to the metabolic diseases of its human host. However, the role of A. muciniphila in the host’s intestinal health remains ambiguous. Here, we comprehensively summarize and discuss the characteristics, the distribution, and the colonization of A. muciniphila in the human gastrointestinal tract (GIT). We propose that the application of A. muciniphila as a biomarker for longevity, for diagnostics and prognostics of intestinal diseases, or for intestinal health should be cautiously considered. Precise dietary regulation can mediate the treatment of intestinal diseases by altering the abundance of A. muciniphila. Although the beneficial role of A. muciniphila and its component in intestinal inflammation has been discovered, in gnotobiotic mice with specific gut microbiota, certain genotype, and colorectal cancer, or in animal models infected with a specific pathogen, A. muciniphila may be related to the occurrence and development of intestinal diseases. Genomic analysis, emphasizing the strain-level phylogenetic differences of A. muciniphila, indicates that a clear description and discussion of each strain is critical before its practical application. Our review provides much needed insight for the precise application of A. muciniphila.