The human gut symbiont Ruminococcus gnavus displays strain-specific exopolysaccharides modulating the host immune response
Victor Laplanche, Samantha Armiento, Immacolata Speciale, Tanja Šuligoj, Emmanuelle H. Crost, Dimitra Lamprinaki, Laura Vaux, Kathryn Gotts, Cristina De Castro, Nathalie Juge
Abstract
Ruminococcus gnavus is a prevalent member of the human gut microbiota and over-represented in inflammatory bowel diseases. R. gnavus ATCC 29149 was previously shown to produce a pro-inflammatory exopolysaccharide (EPS) referred to here as glucorhamnan-I or EPS 29149 . Here, we determined the structure of the polysaccharides from R. gnavus ATCC 35913 (EPS 35193 ) and E1 (EPS E1 ) strains, both consist of a repeating unit with a backbone composed of four α-L-rhamnose units, with alternate 2- and 3-linkages, and a β- d -glucose residue linked to O-2 of one 3-Rha as side branch. This structure differs from EPS 29149 and is referred to as glucorhamnan-II. EPS 35193 and EPS E1 showed variation in the glucosylation level that is non-stochiometric in EPS 35193. R. gnavus strains and their purified EPS induced strain-specific production of cytokines and chemokines in bone-marrow derived dendritic cells and NF-κB activation in reporter cells. R. gnavus ATCC 35913 was the most immunogenic strain, likely due to the absence of an additional capsular polysaccharide layer as shown by TEM, while EPS 29149 , EPS 35193 and EPS E1 showed activation of TLR4 reporter cells. These strain-specific differences in R. gnavus cell surface glycosylation and host response underscore the importance of studying R. gnavus -host interaction at the strain level.