The benefit of consuming dietaryfibers as a part of the daily menu is now well established. However, the roleof the human-colonic microorganisms that degrade this substrate in the humangut remains mostly unclear. Recently, two fiber-degrading bacterial specieswere isolated from human faecal samples, i.e.,Ruminococcus champanellensisandRuminococcus bromii. Previous studies have shown thatR.champanellensisis a cellulolytic bacterium whileR. bromiiis anamylolytic bacterium. Bioinformatics analysis has revealed that bothR.champanellensisandR. bromiiappear to be cellulosome-producingbacteria. In the current study, a new set of cohesin-dockerin interactions werediscovered in both species.
We selected 22 out of 62 predicteddockerins fromR. champanellensisand 11 out of 26 fromR. bromiiwere used as representative dockerins. All of the selected dockerins weretested against the 12 cohesins ofR. champanellensisand the fourcohesins ofR. bromiiin addition to another 13 cohesins from sixdifferent species. The new cohesin-dockerin interactions were discovered usinga cellulose-based microarray method followed by an ELISA method as a subsequentconfirmation.
In total, 69 interactions were identified, outof the 308 intra-species and the 649 inter-species interactions tested.R.champanellensisdockerins showed three affinity profiles which led us topropose two types of cellulosome architectures, cell-bound and cell-free. TheR.bromiidockerins tested exhibited essentially the same binding profile ofinteraction with the fourR. bromiicohesins. Therefore, the existenceof an ‘amylosome’ complex, analogous to the cellulosome, was suggested.
The finding of new mechanisms forutilization of complex carbohydrates in the human colon can assist in futurepharmacological and biotechnological implications. Furthermore, our findingscontribute to our knowledge concerning the role of these two bacteria in the humangut.
