l-Glucitol Catabolism inStenotrophomonas maltophiliaAc

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.