Editors' ChoiceMicrobiome

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Science Translational Medicine  03 Aug 2016:
Vol. 8, Issue 350, pp. 350ec125
DOI: 10.1126/scitranslmed.aah3548

Gut microbiota exist in a mutualistic relationship with the host and play an important role in normal gastrointestinal physiology, such as gastrointestinal transit, visceral sensation, epithelial barrier, and immune function. The communication between microbes and the host is bidirectional and complex, but the mechanics of signaling between them and the directionality of the effect are just being unraveled. Roager et al. now show that gastrointestinal transit time can influence gut microbiota composition and function. They found that slower colonic transit is associated with an increase in microbial diversity. However, although increased microbial diversity is usually thought to reflect a healthy gut microbial ecosystem, this study sheds doubt on the universality of such a claim.

In addition to an increase in microbial diversity, the authors found that the longer transit time was associated with a potentially deleterious switch in microbial metabolism, with increased protein catabolism, decreased polyphenol conversion and mucus secretion, and metabolites reflective of decreased epithelial turnover. However, the shift in metabolism may also represent an adaptation to host function, and it would be interesting to know if these changes help perpetuate the host phenotype and provide an environment conducive for the altered microbial community. In addition, not all protein catabolism is deleterious. For example, the increase in tryptophan metabolism promotes the formation of indole derivatives, which can act as aryl hydrocarbon receptor ligands and have anti-inflammatory properties.

The study highlights the importance of considering host physiological factors when evaluating changes in the microbiome and paves the way for future studies on mutual reinforcement of host-microbial interactions. This should be especially relevant for research evaluating gut microbiota in patients with inflammatory and functional gut disorders, where transit time is not usually accounted for when describing microbial changes.

H. M. Roager et al., Colonic transit time is related to bacterial metabolism and mucosal turnover in the gut. Nat. Microbiol. 10.1038/nmicrobiol.2016.93 (2016). [Abstract]

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