Introduction One of the mostmicrobial rich niches is located in the human body. The Gram-negative anaerobe Akkemansia muciniphila, which belongs tothe Planctomycetes-Verrucomicrobia-Chlamydiae superphylum, is found in the alimentarycanal of more than 90% of the evaluated cases. A. muciniphila is well adapted to the human gut environment anduses glycosolated proteins of the epithelial mucus layer as its C and N source.A study which is conducted earlier suggests that the health of the gastrointestinal tract is correlated with theabundance of A.
muciniphila. For example, whenthe density of A. muciniphila is lowthis is associated to diabetes type 1, Crohn’s disease (CD) and in Ulcerativecolitis (UC). Furthermore, the recovery of the mucus layer in the human colonand decreasing endotoxemia are accociated with A. muciniphila. State of the art There is not muchknown about the interactions between A.muciniphila and the host, nor how it handles the different environmentalcircumstances. Previous studies do suggest that there is a positive consequencefor the health of the gastrointestinaltract when A.
muciniphila is present, butfurther investigation is needed for future application. The interaction of thebacteria and its hosts starts with colonizing in whichthey can adhere by binding to the mucus layer of the intestines epithelium or viathe cells underneath, the enterocytes. It is unclear to which components A. muciniphila binds neither has been studies whether it isable survive in an oxygen rich setting. This study will answer which mechanisms A.
muciniphila uses to adhereto the mucus layer or the epithelium cells of the gastrointestinal tract. Recent findings Although the humancolon mainly consists out of an anaerobic microbe community, doesn’t mean thatall microbes are intolerent to oxygen. The results suggest that A. muciniphila is able to cope in oxicand anoxic environments. As A.
muciniphila is aerotolerant, contrasting incubation conditions were compared in an adhesionexperiment. The binding efficiency with epithelial cells HT29 and Caco-2 do not differ between aerobicand anaerobic atmosphere. Thus, A.muciniphila does not have to be treated as a true anaerobe, but is able tocope with oxygen. Also, it turnedout that the only significant binding of A.muciniphila, compared to BSA, occurred with laminin. The bindingprocess of A.
muciniphila with other extracellular matrix (ECM) proteins, was not significant. Asthe adhesion between A. muciniphila andthe intestinal mucus is less than 1%, it can be stated that there is noadhesion at all.
Several bacteria are known for binding to the colonic mucusand therefor it was unexpected that A.muciniphila did not attach to the colonic mucus. An explanation for this isthat these species do not utilize and degrade the mucus, like A. muciniphila does. Although the adhesionof A. muciniphila and L. rhamnosus on colonic mucus was notcompareble, A. muciniphila adhered toboth enterocrytes equally well as L.
rhamnosus. This might indicate that the enterocytes are true binding sitesfor A. muciniphila. A.
muciniphila and B. fragilis were both cocultivated for 24 hours and indicated an expansionin transepithelial electricalresistance (TER). Compared to the Caco-2 cultures, without bacteria the TER ofCaco-2 cocultures of Escherichia coli declinedsignificantly. This shows that at this timepoint E. coli cells increased and that there is no cell interruption forthe OD600 values of A.muciniphila and B.
fragilis,which indicates a stagnation of growth. The positive impact of cell monolayerintegrity for the first 24 hours was the most succesfull with B. fragilis, followed by A. muciniphila.After 48 hours the transepithelialelectrical resistance ofCaco-2 cocultures of A. muciniphila becameequal to the cocultures of B.fragilis.
During the 48 hour incubation the cell density of B. fragilis andA. muciniphila did not diversify, neither seems that the bacteria areseverly affected.
Under the same circumstances, E. coli affected TERdevelopment negatively. During thesecond 24 hours the coculture increased, suggesting that the transepithelial electrical resistance in E. coli cocultures will furtherdecline.
Earlier studieshave associated obesity and diabetes to decreased gut health and inflammation,which result in lipopolysaccharide (LPS) induced endotoxemia. When LPS is released,enterocytes start producing the chemokine interleukin-8 (IL-8) which leads toinflammation. Needless inflammation can cause disorder in the intestinalepithelium and can disturb the homeastasis of the colonal mucus. The productionof IL-8 in HT-29 cells was lower in A.muciniphila when compared tothe IL-8 production of E.
coli. Thus, there will be no stronginflammation when A. muciniphila is present in the gastrointestinal tract. Because in thepresence of A. muciniphila alsmost no inflammatory reaction was induced, itwas checked wether it does or does not produce LPS and whether it is differentcompared to E. coli. The results show that A.
muciniphila doesproduce LPS, however it does not activate HT-29 cells to produce a lot of interleukin-8. Thereforit is likely that the produced LPS by A.muciniphila is differentcompared to that of E. coli.
Discussion The results showthat A. muciniphila does not bind to the intestinal mucus but prefersto bind to the epithelial cells Caco-2 and HT-29 and the ECM laminin. It remains unknown how thisorganism is able to live in this continually adjusting habitat and should befurther investigated to answere this question. A possible justification why A.
muciniphila is not able to effectivelybind to the intestinal mucus is because A.muciniphila might release a certain stimulus which attacks the mucus. As A. muciniphila was able to connect tothe extracellular matrix laminin it might suggest that pathogens are competingwith A. muciniphila for bindingsitesat locations where the epithelial cell layer of the colon is damaged.
Furthermore, it is likely that A. muciniphila is able to strengthen the barrier of the intestinaltrack. Future research could study the helpful role of A. muciniphila in connection with its host in for example obesityand diabetes.