d-Arabitol Catabolic Pathway in Klebsiella aerogenes

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Klebsiella aerogenes strain W70 has an inducible pathway for the degradation of d-arabitol which is comparable to the one found in Aerobacter aerogenes strain PRL-R3. The pathway is also similar to the pathway of ribitol catabolism in that it is composed of a pentitol dehydrogenase, d-arabitol dehydrogenase (ADH), and a pentulokinase, d-xylulokinase (DXK). These two enzymes are coordinately controlled and induced in response to d-arabitol, the apparent inducer of synthesis of these enzymes. We obtained mutants which lacked a functional d-xylose pathway and were constitutive for the ribitol catabolic pathway. These mutants were able to grow on the unusual pentitol, xylitol, only if they contained the functional DXK of the d-arabitol pathway. This provided us with a specific selection technique for DXK+ transductants. As in A. aerogenes, mutants constitutive for ADH were able to use this enzyme to convert the hexitol d-mannitol to d-fructose. With mutants blocked in the normal d-mannitol catabolic pathway, growth on d-mannitol became a test for ADH constitutivity. Growth of such mutants on xylitol, d-arabitol, and d-mannitol was utilized to classify transductants in mapping, by transductional analysis, the loci involved in d-arabitol utilization. Three-point crosses gave the order dalK-dalD-dalC, where dalK is the DXK structural gene, dalD is the ADH structural gene, and dalC is a regulatory site controlling synthesis of both enzymes.

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