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J Bacteriol. Aug 1968; 96(2): 447–456.
PMCID: PMC252317
Mutants of Aerobacter aerogenes Capable of Utilizing Xylitol as a Novel Carbon1
T. T. Wu,2 E. C. C. Lin,3 and S. Tanaka4
Department of Biological Chemistry, Harvard Medical School, Boston, Massachusetts 02115
Department of Bacteriology and Immunology, Harvard Medical School, Boston, Massachusetts 02115
2 Present address: Department of Biomathematics, Cornell University Graduate School of Medical Sciences, New York, N.Y. 10021.
3 Supported by a Research Career Development Award from the Public Health Service.
4 Present address: Department of Nutritional Pathology, Tokushima University Medical School, Tokushima, Japan.
1 Part of this work was presented before the American Society of Biological Chemists, Atlantic City, N.J., 1966 (Federation Proc. 25:338, 1966).
Abstract
Wild-type Aerobacter aerogenes 1033 is unable to utilize xylitol. A succession of mutants was isolated capable of growth on this compound (0.2%) at progressively faster rates. Whereas the ability to utilize xylitol was achieved in the first-stage mutant (X1) by constitutive production of ribitol dehydrogenase (for which xylitol is a substrate but not an inducer), the basis for enhanced utilization of xylitol in the second-stage mutant (X2) was an alteration of ribitol dehydrogenase. This enzyme was purified from the various mutants. The apparent Km for xylitol was 0.12 m with X2 enzyme and 0.29 m with X1 enzyme. The X2 enzyme was also less heat stable and, at 0.05 m substrate concentration, had a higher ratio of activity with xylitol compared to ribitol than did the X1 enzyme. The third mutant (X3), with an even faster growth rate on xylitol, produced a ribitol dehydrogenase indistinguishable physically or kinetically from that of X2. However, X3 produced constitutively an active transport system which accepts xylitol. The usual function of this system is apparently for the transport of d-arabitol since the latter is not only a substrate but also an inducer of the transport system in parental strains of X3. The sequence of mutations described herein illustrates how genes belonging to different metabolic systems can be mobilized to serve a new biochemical pathway.
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