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Highly adaptable genome in gut bacterium key to intestinal health

a diet high in complex carbohydrates and low in simple sugars. Ten days later, the activity of all genes in the bacterial genome was surveyed in B. theta from the mice's guts.

The research team found that 1,237 of the bacterium's 4,779 genes were highly active compared to B. theta grown in a simple-sugar soup. The predominant group of high-activity genes were involved in the acquisition and digestion of carbohydrates.

"In mice fed complex carbohydrates, we found that the microbes attached to small food particles in the intestine," Gordon says. "These carbohydrate-rich particles are the bacteria's dining room tables. By generating a series of carbohydrate-binding proteins on its outer surface, B. theta is able to hold onto a seat at the table. The bacterium also produces the necessary utensils to break different types of carbohydrate chains into 'bite-sized' pieces; the utensils are a variety of enzymes directed at different types of carbohydrates."

When a set of germ-free mice were fed a simple-sugar diet--instead of a complex-carbohydrate diet--and then inoculated with B. theta, the genome activity analysis showed that B. theta had adaptively switched on a different set of genes encoding surface proteins and carbohydrate-busting enzymes. This switch allowed B. theta to bind to and digest the host-produced mucus carbohydrates.

"By changing its digestive enzymes and surface proteins, the bacterium changed its dining room seating from food particles to the mucus that normally overlies intestinal lining cells," Gordon says. "Mucus represents a consistent source of backup food in the intestinal environment. B. theta's adaptive foraging behavior benefits the bacterium and presumably helps maintain the stability of the microbial society that it is an integral part of."

The dietary switch also caused B. theta to change the activity of genes that code for components of its outer surface cell capsule. This change in the face of this f
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Source:Washington University School of Medicine


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