Dietary carbohydrates alter immune-modulatory functionalities and DNA inversions in Bacteroides thetaiotaomicron

The environment of gut bacteria is extremely dynamic. Environmental conditions were shown to affect microbial composition, however, their effects on bacterial functionality (e.g., immune-modulation activity) are mostly overlooked. Distinct strains of the same species, and even the same bacterial strain, may have different effects on the immune system depending on their growth environment. Therefore, studying the functionality of strains, under different conditions, is crucial. We analyzed functional alterations in the gut symbiont Bacteroides thetaiotaomicron (B. theta) under different diets in humans, under sugar consumption in mice, and in response to 190 different carbon sources in vitro. Dietary alterations affected the orientation of phase variable promoters in B. theta in humans, in vivo and in vitro and altered B. theta’s proteome and immune-modulatory functionality. Studying the effects of dietary components on the immune-modulatory functionalities of key members of the gut microbiota will allow tailored dietary recommendations to patients.