Spondyloarthritis (SpA), is a collective term for a series of chronic joint diseases that differ from the most common form of chronic inflammatory arthritis, viz. Rheumatoid arthritis. Ankylosing spondylitis (AS) is considered to be the prototype within the concept SpA disease and is associated with inflammation of the spine, joints and tendons. This disease is also characterized by the substantial formation of new bone tissue, which may lead to total ankylosis (stiffening) of the spine. Other variants are reactive arthritis, arthritis in patients with inflammatory bowel disease (IBD), and some forms of psoriatic arthritis. The relationship between chronic forms of intestinal inflammation and spondyloarthritis has long been known. Both diseases often occur together and there is a clear overlap between their genetic predisposition. In animal models of SpA, it was observed that the intestinal flora plays a crucial role in the development of the disease. The present proposal is also intended to examine the extent to which the microbial composition of the gut (the microbiome) is associated with the development and progression of SpA. This project is an example of cross-border research with clinical and biotechnological expertise together to examine how gut bacteria can affect a chronic disease.