thetaiotaomicron

Bacteroides thetaiotaomicron, commonly referred to as B. thetaiotaomicron, is a gram-negative, non-spore-forming, obligate anaerobe that colonizes the mammalian gastrointestinal tract. It is one of the most abundant and well-characterized members of the human gut microbiota, particularly within the colon.

The genome has been sequenced and reveals a large repertoire of carbohydrate-active enzymes enabling the digestion of diverse polysaccharides. Central to this capability are polysaccharide utilization loci (PULs) that coordinate enzymes with outer membrane transport proteins. A well-studied subsystem, the starch utilization system, or Sus-like system, illustrates how B. thetaiotaomicron binds, degrades, and imports complex carbohydrates.

Metabolically, the bacterium ferments polysaccharides to short-chain fatty acids such as acetate and propionate, which contribute to host energy balance and gut physiology. It also interacts with the mucosal layer by degrading certain host-derived glycans, influencing the composition and activity of the gut community and shaping immune responses through microbe-host signaling and metabolite production.

In research, B. thetaiotaomicron serves as a model organism for studying gut carbohydrate metabolism and host–microbe interactions. It is genetically tractable and has been used to investigate how microbial gene clusters adapt to diet and how microbial networks influence gut ecology.

Ecologically, B. thetaiotaomicron is a common commensal in healthy humans. While typically non-pathogenic, it can cause infections in severely immunocompromised individuals and in certain clinical contexts. Its study has advanced understanding of gut microbiota function and diet-microbe interactions.