Ruminococcus gnavus is a type of bacterium commonly found within the human gut microbiome. It is a Gram-positive anaerobe first identified in human feces in 1974. It is present in over 90% of individuals, typically making up about 0.1% of the gut microbiota in healthy adults.
The Dual Role of Ruminococcus Gnavus in the Gut
Ruminococcus gnavus is classified as a pathobiont, meaning it can exist harmlessly or offer benefits, yet contribute to health issues. A primary function of this bacterium involves the degradation of mucus, which forms a protective layer lining the intestinal tract. This process is a normal part of gut health, as R. gnavus strains utilize mucin glycans, such as sialic acid and fucose, as a food source.
However, the balance can shift if there is an overgrowth or if specific strains of R. gnavus become dominant. Certain strains can excessively break down the protective mucus layer, potentially exposing the underlying intestinal cells. This degradation of mucus is associated with conditions where gut barrier integrity is compromised. The bacterium also metabolizes compounds, including bile acids, which can further influence the gut environment and host metabolism.
Association with Inflammatory Conditions
An increased abundance of Ruminococcus gnavus, often referred to as a “bloom,” has been observed in individuals with inflammatory bowel disease (IBD), including both Crohn’s disease and ulcerative colitis. Its prevalence is higher in patients with active IBD, and its abundance can increase significantly during disease flares, suggesting a connection to intestinal inflammation severity.
A key mechanism linking R. gnavus to inflammation involves its production of a specific inflammatory polysaccharide known as glucorhamnan. This complex sugar molecule can trigger an immune response in the host. Glucorhamnan induces the secretion of pro-inflammatory cytokines, such as TNFα, by dendritic cells. This activation pathway depends on toll-like receptor 4 (TLR4), indicating a direct molecular interaction with the host’s immune system.
Beyond IBD, R. gnavus has been associated with other inflammatory conditions. Elevated levels are noted in spondyloarthritis, a group of inflammatory diseases primarily affecting the spine and joints. It is also found in individuals with systemic lupus erythematosus (SLE), an autoimmune disease causing widespread inflammation. It has also been linked to allergic conditions, including eczema and food allergies, particularly in infants.
Factors That Influence Ruminococcus Gnavus Levels
Diet plays a role in modulating Ruminococcus gnavus levels and activity within the gut microbiome. A Western-style diet, characterized by high amounts of fat and simple sugars, has been associated with an increased abundance of R. gnavus. This dietary pattern can alter the gut microbial community, favoring the growth of mucus-degrading bacteria like R. gnavus. Such diets lack sufficient dietary fiber, which prompts certain gut bacteria to utilize the host’s mucus layer as an alternative energy source.
Conversely, diets rich in dietary fiber and complex carbohydrates support a more balanced gut microbiome. Dietary fibers provide fermentable substrates for a diverse range of beneficial gut bacteria. This promotes the growth of microbes that produce beneficial compounds, such as short-chain fatty acids, and helps maintain the integrity of the intestinal mucus layer. By fostering a microbial environment where beneficial bacteria thrive, adequate fiber intake helps keep R. gnavus levels in check and supports overall gut health.