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The bovine gastrointestinal tract is the main reservoir for enterohaemorrhagicEscherichia coli(EHEC) responsible for food-borne infections. Characterization of nutrients that promote the carriage of these pathogens by the ruminant would help to develop ecological strategies to reduce their survival in the bovine gastrointestinal tract. In this study, we show for the first time that free ethanolamine (EA) constitutes a nitrogen source for the O157:H7 EHEC strain EDL933 in the bovine intestinal content because of induction of theeut(ethanolamineutilization) gene cluster. In contrast, theeutgene cluster is absent in the genome of most species constituting the mammalian gut microbiota. Furthermore, theeutBgene (encoding a subunit of the enzyme that catalyses the release of ammonia from EA) is poorly expressed in non-pathogenicE. coli. Accordingly, EA is consumed by EHEC but is poorly metabolized by endogenous microbiota of the bovine small intestine, including commensalE. coli. Interestingly, the capacity to utilize EA as a nitrogen source confers a growth advantage toE. coliO157:H7 when the bacteria enter the stationary growth phase. These data demonstrate that EHEC strains take advantage of a nitrogen source that is not consumed by the resident microbiota, and suggest that EA represents an ecological niche favouring EHEC persistence in the bovine intestine.