Eubacterium limosum is a type of anaerobic bacterium, meaning it thrives in environments completely free of oxygen. This rod-shaped microorganism was first described in 1935 and is a common inhabitant of the human gut and animal digestive tracts. Its presence in the gut microbiome has drawn scientific attention due to its metabolic processes and influence on host health. This bacterium is classified under the phylum Firmicutes and is recognized for its role in converting dietary compounds.
Distinct Metabolic Capabilities
Eubacterium limosum performs acetogenesis, producing acetate. It utilizes the Wood-Ljungdahl pathway, an efficient method for fixing single-carbon (C1) compounds. Through this pathway, it converts substrates like carbon dioxide (CO2), hydrogen (H2), carbon monoxide (CO), or methanol into acetate.
Some strains also produce other compounds like butyrate and hexanoate. Growth on glucose or methanol can lead to butyrate formation. The ability to utilize diverse C1 feedstocks and produce short-chain fatty acids highlights its metabolic versatility and potential for industrial applications in biotechnology.
Contribution to the Gut Microbiome
Eubacterium limosum is a natural resident of the gut, contributing to the gut environment through its metabolic activities. As an acetogen, it produces acetate, a short-chain fatty acid (SCFA), which serves as an energy source for host cells and other gut microbes. This bacterium also plays a role in maintaining low concentrations of hydrogen in the gut, which can facilitate interspecies hydrogen transfer within the microbial community.
The production of SCFAs like acetate and butyrate by E. limosum influences the stability and diversity of the gut ecosystem. These fatty acids contribute to a balanced gut pH and can support the growth of other beneficial bacteria. Its presence has been observed to be higher in centenarians, suggesting a potential association with a healthy aging microbiome.
Impact on Human Health
The metabolic products of Eubacterium limosum, particularly short-chain fatty acids like butyrate, affect human health. Butyrate, for example, can act as an anti-inflammatory agent, reducing inflammatory markers like IL-6 and TLR4 expression in colon cells. This anti-inflammatory effect suggests a potential role in managing inflammatory bowel diseases (IBD) like colitis. Studies have shown that administering E. limosum can ameliorate experimental colitis by increasing cecal butyrate levels and improving mucosal integrity.
Beyond its local gut effects, E. limosum has been linked to broader physiological outcomes. It participates in the demethylation of dietary compounds, including lignans and L-carnitine. The demethylation of L-carnitine by E. limosum can prevent the formation of trimethylamine (TMA), a precursor to trimethylamine-N-oxide (TMAO), which is associated with atherosclerosis and cardiovascular disease. This suggests a potential protective role against cardiovascular issues by influencing systemic metabolite levels.
Factors Influencing Its Abundance
The abundance and activity of Eubacterium limosum in the gut are influenced by several factors, including dietary components and the gut environment. Dietary fibers and prebiotics can promote its growth and activity, as these provide substrates for its metabolic processes. Germinated barley foodstuff, a prebiotic, has been shown to increase the number of E. limosum in the stool of individuals with ulcerative colitis, alongside an increase in butyrate production.
Antibiotics can alter the overall gut microbial composition, potentially impacting the presence of E. limosum. Since it is a strict anaerobe, its viability can be affected by oxygen exposure, which might influence its ability to reproduce in the gastrointestinal tract. Lifestyle factors, such as diet and exercise, are also known to influence the broader gut microbiota, which in turn can affect the niche and prevalence of specific bacteria like E. limosum.