Novel Odoribacter splanchnicus Strain and Its Outer Membrane Vesicles Exert Immunoregulatory Effects in vitro

Abstract

<i>Odoribacter splanchnicus</i>, belonging to the order Bacteroidales, is a common, short-chain fatty acid producing member of the human intestinal microbiota. A decreased abundance of <i>Odoribacter</i> has been linked to different microbiota-associated diseases, such as non-alcoholic fatty liver disease, cystic fibrosis and inflammatory bowel disease (IBD). The type strain of <i>O. splanchnicus</i> has been genome-sequenced, but otherwise very little is known about this anaerobic bacterium. The species surfaces in many microbiota studies and, consequently, comprehension on its interactions with the host is needed. In this study, we isolated a novel strain of <i>O. splanchnicus</i> from a healthy fecal donor, identified it by genome sequencing and addressed its adhesive, epithelium reinforcing and immunoregulatory properties. Our results show that <i>O. splanchnicus</i> strain 57 is non-adherent to enterocytes or mucus, does not reinforce nor compromise Caco-2 monolayer integrity and most likely harbors penta-acylated, less endotoxic lipid A as part of its lipopolysaccharide (LPS) structure based on the lack of gene <i>lpxM</i> and <i>in vitro</i> results on low-level NF-κB activity. The studies by transmission electron microscopy revealed that <i>O. splanchnicus</i> produces outer membrane vesicles (OMV). <i>O. splanchnicus</i> cells, culture supernatant i.e., spent medium or OMVs did not induce interleukin-8 (IL-8) response in HT-29 enterocyte cells suggesting a very low proinflammatory capacity. On the contrary, the treatment of HT-29 cells with <i>O. splanchnicus</i> cells, spent medium or OMVs prior to exposure to <i>Escherichia coli</i> LPS elicited a significant decrease in IL-8 production as compared to <i>E. coli</i> LPS treatment alone. Moreover, <i>O. splanchnicus</i> spent supernatant induced IL-10 production by immune cells, suggesting anti-inflammatory activity. Our <i>in vitro</i> findings indicate that <i>O. splanchnicus</i> and its effector molecules transported in OMVs could potentially exert anti-inflammatory action in the gut epithelium. Taken together, <i>O. splanchnicus</i> seems to be a commensal with a primarily beneficial interaction with the host.