Carbon nutrition of pathogenic and commensal E. coli

Transcriptome profiling of E. coli MG1655, E. coli EDL933, E. coli ECOR26, and E. coli Nissle 1917 grown on mouse cecal mucus as carbon source The carbon sources that support growth of pathogenic E. coli O157:H7 in the mammalian intestine have not previously been investigated. In vivo, pathogenic E. coli EDL933 primarily grows as dispersed single cells within the mucus layer that overlies the mouse cecal epithelium. We therefore compared the pathogen and commensal E. coli MG1655 for their mode of metabolism in vitro on a mixture of the sugars known to be present in cecal mucus and found that the two strains used the thirteen sugars in a similar order and co-metabolized as many as nine sugars at a time. We conducted a systematic mutational analysis of E. coli EDL933 and E. coli MG1655 with lesions in the pathways used for catabolism of thirteen mucus-derived sugars and five other compounds for which the corresponding gene system was induced in the transcriptome of cells grown on cecal mucus. Each of 18 catabolic mutants in both genetic backgrounds was fed to streptomycin-treated mice together with the respective wildtype parent strain and their colonization was monitored in fecal plate counts. None of the mutations corresponding to the five compounds not found in mucosal polysaccharides resulted in colonization defects. Based on the mutations that caused colonization defects, we determined that both E. coli EDL933 and E. coli MG1655 used arabinose, fucose, and N-acetylglucosamine in the intestine. In addition, E. coli EDL933 used galactose, hexuronates, mannose and ribose, whereas E. coli MG1655 used gluconate and N-acetylneuraminic acid. The colonization defects of six catabolic lesions were found to be additive in E. coli EDL933, but not E. coli MG1655. The data indicate that pathogenic E. coli EDL933 uses sugars that are not used by commensal E. coli MG1655 to colonize the mouse intestine. The results suggest a strategy whereby invading pathogens gain advantage by simultaneously consuming several sugars that may be available because they are not consumed by the commensal intestinal microbiota. Keywords: growth condition: carbon source was mouse cecal mucus E. coli strains were grown on MOPS minimal medium containing 10 mg/ml of mucus or 0.2% glucose in 10 ml standing culture in testtubes and harvested at OD600 = 0.4.