Ribitol Catabolic Pathway in Klebsiella aerogenes

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RESUMO

In Klebsiella aerogenes W70, there is an inducible pathway for the catabolism of ribitol consisting of at least two enzymes, ribitol dehydrogenase (RDH) and d-ribulokinase (DRK). These two enzymes are coordinately controlled and induced in response to d-ribulose, an intermediate of the pathway. Whereas wild-type K. aerogenes W70 are unable to utilize xylitol as a carbon and energy source, mutants constitutive for the ribitol pathway are able to utilize RDH to oxidize the unusual pentitol, xylitol, to d-xylulose. These mutants are able to grow on xylitol, presumably by utilization of the d-xylulose produced. Mutants constitutive for l-fucose isomerase can utilize the isomerase to convert d-arabinose to d-ribulose. In the presence of d-ribulose, RDH and DRK are induced, and such mutants are thus able to phosphorylate the d-ribulose by using the DRK of the ribitol pathway. Derivatives of an l-fucose isomerase-constitutive mutant were plated on d-arabinose, ribitol, and xylitol to select and identify mutations in the ribitol pathway. Using the transducing phage PW52, we were able to demonstrate genetic linkage of the loci involved. Three-point crosses, using constitutive mutants as donors and RDH−, DRK− double mutants as recipients and selecting for DRK+ transductants on d-arabinose, resulted in DRK+RDH+-constitutive, DRK+RDH+-inducible, and DRK+RDH−-inducible transductants but no detectable DRK+RDH− constitutive transductants, data consistent with the order rbtC-rbtD-rbtK, where rbtC is a control site and rbtD and rbtK correspond to the sites for the sites for the enzymes RDH and DRK, respectively.

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