L-fucose stimulates utilization of D-Ribose by Eschetichia coli MG1655 ΔfucAO and E-coli nissle 1917 ΔfucAO mutants in the mouse intestine and in m9 minimal medium

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 Delta fucAO mutant and an E. coli MG1655 Delta rbsK mutant were fed separately to mice along with wild-type E. coli MG1655. The E. coli MG1655 Delta fucAO mutant colonized the intestine at a level 2 orders of magnitude lower than that of the wild type, but the E. coli MG1655 Delta rbsK mutant and the wild type colonized at nearly identical levels. Surprisingly, an E. coli MG1655 Delta fucAO Delta rbsK mutant was eliminated from the intestine by either wild-type E. coli MG1655 or E. coli MG1655 Delta fucAO, suggesting that the Delta 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 Delta fucAO mutant but not by an E. coli MG1655 Delta fucK mutant. Since the Delta fucK mutant cannot convert L-fuculose to L-fuculose-1-phosphate, whereas the Delta fucAO mutant accumulates L-fuculose- I -phosphate, the data suggest that L-fuculose-l-phosphate stimulates growth on ribose both in the intestine and in vitro. An E. coli Nissle 1917 Delta fucAO mutant, derived from a human probiotic commensal strain, acted in a manner identical to that of E. coli MG1655 Delta 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.