d -Arabitol Catabolic Pathway in Klebsiella aerogenes

Abstract

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.