Requirement of Purine and Pyrimidine Synthesis for Colonization of the Mouse Intestine by Escherichia coli

To study the adaptation of an intestinal bacterium to its natural environment, germfree mice were associated with commensalEscherichia coli MG1655. Two-dimensional gel electrophoresis was used to identify proteins differentially expressed inE. coli MG1655 collected from either cecal contents or anaerobicin vitro cultures. Fourteen differentially expressed proteins (>3-fold;P < 0.05) were identified, nine of which were upregulated in cecal versusin vitro -grownE. coli . Four of these proteins were investigated further for their role in gut colonization. After deletion of the corresponding genes, the resultingE. coli mutants were tested for their ability to colonize the intestines of gnotobiotic mice in competition with the wild-type strain. A mutant devoid ofydjG , which encodes a putative NADH-dependent methylglyoxal reductase, reached a 1.2-log-lower cecal concentration than the wild type. Deletion of thenanA gene encodingN -acetylneuraminate lyase affected the colonization and persistence ofE. coli in the intestines of the gnotobiotic mice only slightly. A mutant devoid of 5′-phosphoribosyl 4-(N -succinocarboxamide)-5-aminoimidazole synthase, a key enzyme of purine synthesis, displayed intestinal cell counts >4 logs lower than those of the wild type. Deletion of the gene encoding aspartate carbamoyltransferase, a key enzyme of pyrimidine synthesis, even resulted in the washout of the corresponding mutant from the mouse intestinal tract. These findings indicate thatE. coli needs to synthesize purines and pyrimidines to successfully colonize the mouse intestine.