Akkermansia muciniphila - friend or foe in colorectal cancer?

Akkermansia muciniphila is a gram-negative anaerobic bacterium, which represents a part of the commensal human microbiota. Decline in the abundance of A. muciniphila among other microbial species in the gut correlates with severe systemic diseases such as diabetes, obesity, intestinal inflammation and colorectal cancer. Due to its mucin-reducing and immunomodulatory properties, the use of probiotics containing Akkermansia sp. appears as a promising approach to the treatment of metabolic and inflammatory diseases. In particular, a number of studies have focused on the role of A. muciniphila in colorectal cancer. Of note, the results of these studies in mice are contradictory: some reported a protective role of A. muciniphila in colorectal cancer, while others demonstrated that administration of A. muciniphila could aggravate the course of the disease resulting in increased tumor burden. More recent studies suggested the immunomodulatory effect of certain unique surface antigens of A. muciniphila on the intestinal immune system. In this Perspective, we attempt to explain how A. muciniphila contributes to protection against colorectal cancer in some models, while being pathogenic in others. We argue that differences in the experimental protocols of administration of A. muciniphila, as well as viability of bacteria, may significantly affect the results. In addition, we hypothesize that antigens presented by pasteurized bacteria or live A. muciniphila may exert distinct effects on the barrier functions of the gut. Finally, A. muciniphila may reduce the mucin barrier and exerts combined effects with other bacterial species in either promoting or inhibiting cancer development.

Tenuifilum thalassicum gen. nov., sp. nov., a novel moderate thermophilic anaerobic bacterium from a Kunashir Island shallow hot spring representing a new family Tenuifilaceae fam. nov. in the class Bacteroidia.

A novel anaerobic moderately thermophilic bacterium, designated strain 38H-strT, was isolated from a 12m deep hot spring of the Kunashir Island shore. Gram-negative cells were non-spore-forming, motile, straight or curved filamentous rods, occasionally forming loops and knots. The strain grew at 20-65°C and pH range of 4.0-9.0 with an optimum at 50°C and pH 6.5-7.0. Strain 38H-strT required 0.5-2.5% NaCl (1.5% is an optimum) for growth. It was a chemoorganoheterotroph, growing on carbohydrates (starch, pullulan, alginate, laminarin, beta-glucan) or peptide mixtures and proteins (peptone, tryptone, gelatin, and α- or ß- keratins). Major products of glucose fermentation were acetate, hydrogen, and carbon dioxide. Major cellular fatty acids were iso- and anteiso-C15:0. Phosphatidylethanolamine, an unidentified phospholipid, and three unidentified polar lipids were detected in cellular lipids fractions. The quinone was MK-7. The size of complete genome of strain 38H-strT was 3.2 Mb; DNA G+C content was 38.3mol%. According to 16S rRNA gene sequence and conserved protein sequences phylogenies, strain 38H-strT represented a deeply branched lineage near the root of the class Bacteroidia. Based on phylogenetic analysis and phenotypic features the novel isolate was assigned to a novel family within the order Bacteroidales for which the name Tenuifilaceae fam. nov. is proposed. Strain 38H-strT (=DSM 100343T =VKM B-2964T) represents the first genus and species Tenuifilum thalassicum gen. nov., sp. nov.