l -Fucose Stimulates Utilization of d -Ribose by Escherichia coli MG1655 Δ fucAO and E. coli Nissle 1917 Δ fucAO Mutants in the Mouse Intestine and in M9 Minimal Medium

Abstract

ABSTRACT Escherichia coli MG1655 uses several sugars for growth in the mouse intestine. To determine the roles of l -fucose and d -ribose, an E. coli MG1655 Δ fucAO mutant and an E. coli MG1655 Δ rbsK mutant were fed separately to mice along with wild-type E. coli MG1655. The E. coli MG1655 Δ fucAO mutant colonized the intestine at a level 2 orders of magnitude lower than that of the wild type, but the E. coli MG1655 Δ rbsK mutant and the wild type colonized at nearly identical levels. Surprisingly, an E. coli MG1655 Δ fucAO Δ rbsK mutant was eliminated from the intestine by either wild-type E. coli MG1655 or E. coli MG1655 Δ fucAO , suggesting that the Δ fucAO mutant switches to ribose in vivo. Indeed, in vitro growth experiments showed that l -fucose stimulated utilization of d -ribose by the E. coli MG1655 Δ fucAO mutant but not by an E. coli MG1655 Δ fucK mutant. Since the Δ fucK mutant cannot convert l -fuculose to l -fuculose-1-phosphate, whereas the Δ fucAO mutant accumulates l -fuculose-1-phosphate, the data suggest that l -fuculose-1-phosphate stimulates growth on ribose both in the intestine and in vitro. An E. coli Nissle 1917 Δ fucAO mutant, derived from a human probiotic commensal strain, acted in a manner identical to that of E. coli MG1655 Δ fucAO in vivo and in vitro. Furthermore, l -fucose at a concentration too low to support growth stimulated the utilization of ribose by the wild-type E. coli strains in vitro. Collectively, the data suggest that l -fuculose-1-phosphate plays a role in the regulation of ribose usage as a carbon source by E. coli MG1655 and E. coli Nissle 1917 in the mouse intestine.