l -Glucitol Catabolism in Stenotrophomonas maltophilia Ac

Abstract

ABSTRACT The carbohydrate catabolism of the bacterium Stenotrophomonas maltophilia Ac (previously named Pseudomonas sp. strain Ac), which is known to convert the unnatural polyol l -glucitol to d -sorbose during growth on the former as the sole source of carbon and energy, was studied in detail. All enzymes operating in a pathway that channels l -glucitol via d -sorbose into compounds of the intermediary metabolism were demonstrated, and for some prominent reactions the products of conversion were identified. d -Sorbose was converted by C-3 epimerization to d -tagatose, which, in turn, was isomerized to d -galactose. d -Galactose was the initial substrate of the De Ley-Doudoroff pathway, involving reactions of NAD-dependent oxidation of d -galactose to d -galactonate, its dehydration to 2-keto-3-deoxy- d -galactonate, and its phosphorylation to 2-keto-3-deoxy- d -galactonate 6-phosphate. Finally, aldol cleavage yielded pyruvate and d -glycerate 3-phosphate as the central metabolic intermediates.