d-Arabitol was observed to be toxic to many laboratory strains of Escherichia coli K-12, and xylitol was found to be toxic to an existing E. coli C mutant strain. Fructose-specific components of the phosphoenolpyruvate:sugar phosphotransferase system are required for xylitol toxicity. Selection for xylitol resistance results in Fru− strains blocked in fructose phosphotransferase. Introduction of the ptsF or ptsI mutation into a xylitol-sensitive strain eliminates sensitivity. [14C]fructose uptake experiments imply that the mutation to xylitol sensitivity, which is co-transducible with ara and leu, results in derepression of normally inducible fructose phosphotransferase. Wild-type strains also become xylitol sensitive if induced by (and then removed from) fructose. Xylitol toxicity is prevented by fructose in both wild-type and mutant strains. Circumstances causing xylitol, a new food additive, to become toxic to an otherwise insensitive wild-type organism have not been reported previously. The d-arabitol-sensitive laboratory strains are galactitol (dulcitol) utilizers, although most other strains are not. Selection for d-arabitol resistance results in Gat− strains blocked in a constitutive galactitol-specific component of the phosphotransferase system. A mutation causing d-arabitol sensitivity occurred many years ago in AB284, the parent of AB311, AB312, AB313, and many other strains. d-Arabitol sensitivity also occurs in sorbitol-constitutive strains and is shown, like the previous two instances of pentitol toxicities, to result from a constitutive phosphotransferase, which is blocked in mutants selected for resistance
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