The human gastrointestinal tract hosts a dense and diverse community of microorganisms, collectively known as the gut microbiome. This intricate ecosystem, particularly in the large intestine, is responsible for a variety of host-microbe interactions that support health. Among the thousands of bacterial species residing there, the Lachnospiraceae family stands out as a highly abundant and significant group. They are considered a core component of this microbial community, participating directly in the metabolic processes that provide sustenance and protection to the host.
Defining the Lachnospiraceae Family
Lachnospiraceae is a phylogenetically diverse family of bacteria classified under the phylum Firmicutes. These bacteria are obligate anaerobes, meaning they thrive in the oxygen-free environment of the colon, and possess a Gram-positive ultrastructure. Their prevalence is remarkable, often comprising between 10% and 45% of the total bacteria found in the feces of healthy adults, cementing their role as one of the most numerous groups in the gut.
The family encompasses numerous genera, including prominent members like Roseburia, Blautia, Coprococcus, and Lachnospira. These different genera exhibit a range of metabolic capabilities, which allows the family as a whole to process a wide variety of substrates. The presence of specialized enzymes, such as glycoside hydrolases, enables them to break down complex carbohydrates that the host cannot digest independently. Lachnospiraceae colonize the intestinal lumen relatively early in life and tend to increase in both species richness and relative abundance as an individual ages.
Primary Function Butyrate Production
The primary function of Lachnospiraceae revolves around the process of microbial fermentation, which results in the production of short-chain fatty acids (SCFAs). These bacteria are adapted to utilize dietary polysaccharides, or fiber, that pass undigested through the upper gastrointestinal tract and enter the colon. They employ carbohydrate-active enzymes to dismantle these complex plant-derived structures, such as inulin, resistant starch, and arabinoxylan.
Fermentation of these non-digestible carbohydrates yields the three main SCFAs: acetate, propionate, and butyrate. Lachnospiraceae are among the foremost producers of butyrate in the human gut, generating it through distinct metabolic pathways. Butyrate itself is a potent molecule, serving as the preferred energy source for colonocytes, which are the epithelial cells lining the colon.
By supplying this energy, butyrate directly supports the proliferation and health of the colonocytes, which in turn reinforces the integrity of the intestinal barrier. A robust gut barrier prevents the translocation of harmful substances and pathogens from the gut lumen into the bloodstream.
Links to Systemic Health and Disease
The metabolic output of Lachnospiraceae, particularly butyrate, provides a direct mechanism by which these bacteria influence the host’s systemic health. Butyrate’s anti-inflammatory properties are well-documented, mediating its effects by modulating immune cell function. It can stimulate the differentiation of T-regulatory cells, which are specialized immune cells that suppress inflammatory responses throughout the body.
A reduction in the abundance of Lachnospiraceae is frequently observed in individuals suffering from inflammatory conditions, such as Inflammatory Bowel Disease (IBD). This decrease in butyrate-producing capacity contributes to the loss of gut barrier function and increased intestinal inflammation characteristic of the disease. Specific genera like Roseburia and Coprococcus are examples of Lachnospiraceae members whose diminished presence correlates with the severity of IBD.
The family’s association with metabolic disorders is nuanced. While some Lachnospiraceae genera, such as Roseburia, are associated with lean individuals and positive metabolic markers, other specific strains have been linked to metabolic disturbances. Research using animal models has shown that certain Lachnospiraceae bacteria can contribute to the development of obesity and insulin resistance, particularly when combined with a high-fat diet. This dual role suggests that the effect on host metabolism is highly dependent on the specific species or strain involved, as well as the overall dietary context.
Influencing Lachnospiraceae Through Diet
Because Lachnospiraceae rely on substrates that the host cannot utilize, their growth and metabolic activity are susceptible to dietary changes. The most effective way to support the population of these beneficial bacteria is through the increased consumption of fermentable fibers, often referred to as prebiotics. These are the complex carbohydrates that reach the large intestine intact, providing the necessary fuel for butyrate production.
Examples of effective fermentable fibers include resistant starch, which is found in foods like cooled potatoes, oats, and legumes. Resistant starch is effective at increasing the abundance of specific butyrate-producing Lachnospiraceae, such as Roseburia. Additionally, non-digestible polysaccharides present in whole grains, fruits, and vegetables serve as substrates that favor the growth of this bacterial family. By consistently supplying these fibers, an individual can selectively enrich the Lachnospiraceae population.