Microbiome Monday: The Colony In Your Colon main content.

Microbiome Monday: The Colony In Your Colon

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Welcome to another Microbiome Monday! The Museum’s new special exhibition The Secret World Inside You is now open, and we're bringing you weekly primers on the human microbiome and the research surrounding it from Curators Rob DeSalle and Susan Perkins, as well as from other scientists who are working in this exciting field.

Last week, we looked at some of the ways microbes are used in food. Many of the microbes that live in the human body, though, are responsible for breaking down food—like a Thanksgiving feast—and turning it into energy we can use. Today, we take a look inside the colon, home to many of these microbes.

By far the largest population of bacteria in the human body is found in the colon. The majority are anaerobic, which means they don’t require oxygen and, of these, species of the genus Bacteroides are among the most common.

A sample of Bacteroides bacteria grown in culture.
Courtesy of the Centers for Disease Control

Outside the gut, strains of Bacteroides can cause abscesses in the abdomen, brain, liver, pelvis, and lungs, as well as bacteremia, an infection of the bloodstream. But in the colon, they serve important functions, breaking down carbohydrates, producing enzymes specifically designed to deal with different foods, and extracting energy from those foods. One species, B. fragilis, appears to stimulate immune cells called regulatory T-cells, which restrain more aggressive inflammatory T-cells, which can trigger colitis and other disorders.

A human T-cell, seen through a scanning electron microscope.
Courtesy of National Institute of Allergy and Infectious Diseases

Researchers are also beginning to tease out the possible relationship between the overall makeup of a person’s gut microbiome and a propensity toward obesity, in which it is suspected Bacteroides may play a role.

In any case, the usefulness and ubiquity of bacteria in the colon probably can’t be overstated. Three-quarters of human feces is water and, of the remaining quarter, one-third is composed of bacteria—or as Giulia Enders, author of Gut: The Inside Story of Our Body’s Most Underrated Organ, describes them, “gut flora that ended their careers in the digestive business and are ready to retire from the workplace.”

A version of this story originally appeared in the Fall issue of the Member magazine Rotunda.