Microbiota-activated PPAR-γ signaling inhibits dysbiotic Enterobacteriaceae expansion

Healthy guts exclude oxygen Normally, the lumen of the colon lacks oxygen. Fastidiously anaerobic butyrate-producing bacteria thrive in the colon; by ablating these organisms, antibiotic treatment removes butyrate. Byndloss et al. discovered that loss of butyrate deranges metabolic signaling in gut cells (see the Perspective by Cani). This induces nitric oxidase to generate nitrate in the lumen and disables β-oxidation in epithelial cells that would otherwise mop up stray oxygen before it enters the colon. Simultaneously, regulatory T cells retreat, and inflammation is unchecked, which contributes yet more oxygen species to the colon. Then, facultative aerobic pathogens, such as Escherichia coli and Salmonella enterica , can take advantage of the altered environment and outgrow any antibiotic-crippled and benign anaerobes. Science , this issue p. 570 ; see also p. 548