Infection marks gut commensals

Bacteroides spp. are members of the gut microbiota with prominent genomic plasticity and adaptability, which suggests that they can genetically adapt to changing environments. Whether enteric infection and inflammation can cause adaptations in gut commensal bacteria is unclear. In this study, Tawk et al. explore the gut microbiota adaptations during infection. They used a combination of population dynamics and in vivo mice assays to show that the gut commensal Bacteroides thetaiotaomicron is stable under healthy conditions. However, when inflammatory infection by the enteropathogen Citrobacter rodentium is established, B. thetaiotaomicron undergoes selection of a single-nucleotide variant in the mouse gut. This variant occurs due to a S173F mutation in the outer membrane protein IctA, which increases the variant fitness compared with the wild-type strain, promoting resistance to oxidative stress. Is this selective sweep in B. thetaiotaomicron only regulated by the enteric pathogen? The authors show that specific commensal species can either inhibit or promote the expansion of the mutant variant, as a result of vitamin B6 levels in the gut lumen. In sum, this work demonstrates the effect of infection and inflammation on the adaptations of the commensal population in the mouse gut.

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