The efficient use of polysaccharides is one of the main features of successful gut commensals, such as Bacteroides thetaiotaomicron, leading to the hypothesis that rapid growth promotes gut engraftment. By contrast, Goodman and colleagues now find that B. thetaiotaomicron requires the alarmone (p)ppGpp, which downregulates several biosynthetic pathways in response to starvation, for the colonization of the mouse gut. A strain in which two (p)ppGpp synthases were deleted could not compete with wild type B. thetaiotaomicron or with several other gut commensals for gut engraftment. (p)ppGpp halts growth and upregulates the tricarboxylic acid cycle, in particular the production of α-ketoglutarate, which is important to survive starvation. This suggests that gut bacteria face temporary nutrient shortages and other stresses, through which they can persist by inducing the stringent response and arresting growth.