Aeromonas hydrophila was examined for fructose and mannose transport systems. A. hydrophila was shown to possess a phosphoenolpyruvate (PEP): fructose phosphotransferase system (fructose-PTS) and a mannose-specific PTS, both induced by fructose and mannose. The mannose-PTS of A. hydrophila exhibited cross-reactivity with Escherichia coli mannose-PTS proteins. The fructose-PTS proteins exhibited cross-reactivities with E. coli and Xanthomonas campestris fructose-PTS proteins. In A. hydrophila grown on mannose as well as on fructose, the phosphorylated derivative accumulated from fructose was fructose 1-phosphate. Identification of fructose 1-phosphate was confirmed by 13C-NMR spectroscopy. 1-Phosphofructokinase (1-PFK), which converts the product of the PTS reaction to fructose 1,6-diphosphate, was present in A. hydrophila grown with fructose but not on mannose. An inducible phosphofructomutase (PFM) activity, an unusual enzyme converting fructose 1-phosphate to fructose 6-phosphate, was detected in extracts induced by mannose or fructose. These results suggest that in cells grown on fructose, fructose 1-phosphate could be converted to fructose 1,6-diphosphate either directly by the 1-PFK activity or via fructose 6-phosphate by the PFM and 6-phosphofructokinase activities. In cells grown on mannose, the degradation of fructose 1-phosphate via PFM and the Embden-Meyerhof pathway appeared to be a unique route.