A Subset of Polysaccharide Capsules in the Human Symbiont Bacteroides thetaiotaomicron Promote Increased Competitive Fitness in the Mouse Gut

Publication date: Available online 28 September 2017
Source:Cell Host & Microbe
Author(s): Nathan T. Porter, Pablo Canales, Daniel A. Peterson, Eric C. Martens
Capsular polysaccharides (CPSs) play multiple roles in protecting bacteria from host and environmental factors, and many commensal bacteria can produce multiple capsule types. To better understand the roles of different CPSs in competitive intestinal colonization, we individually expressed the eight different capsules of the human gut symbiont Bacteroides thetaiotaomicron. Certain CPSs were most advantageous in vivo, and increased anti-CPS immunoglobulin A correlated with increased fitness of a strain expressing one particular capsule, CPS5, suggesting that it promotes avoidance of adaptive immunity. A strain with the ability to switch between multiple capsules was more competitive than those expressing any single capsule except CPS5. After antibiotic perturbation, only the wild-type, capsule-switching strain remained in the gut, shifting to prominent expression of CPS5 only in mice with intact adaptive immunity. These data suggest that different capsules equip mutualistic gut bacteria with the ability to thrive in various niches, including those influenced by immune responses and antibiotic perturbations.

Graphical abstract

Teaser

Symbiotic Bacteroides species encode for multiple capsular polysaccharides, the roles of which have remained poorly defined. Porter et al. identify one capsule involved in competitive colonization of the mouse gut that assists in evading adaptive immune responses. The genes for synthesizing this capsule are frequently identified in human gut samples.


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