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Transport and Catabolism of D-Fructose by Spirillum itersonii

¹ Department of Microbiology, Health Sciences Division, Virginia Commonwealth University, Richmond, Virginia 23298; and Biology Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

ABSTRACT

Spirillum itersonii ATCC 12639 utilized D-fructose but neither D-glucose nor D-gluconate as a sole source of carbon and energy. The substrate saturation kinetics for D-fructose and D-glucose uptake by whole cells indicated the presence of a carrier-mediated transport system for D-fructose but not for D-glucose. The D-fructose uptake activity was induced (10- to 12-fold increase) during growth on D-fructose-Casamino Acids (CA) or D-glucose-CA medium, but not CA alone. D-Fructose uptake activity was stimulated by Na⁺ or Li⁺, but was inhibited by KCN, NaN₃, 2,4-dinitrophenol, and p-chloromercuribenzoate. High specific activities of glucokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydratase, and 2-keto-3-deoxy-6-phosphogluconate aldolase were detected in extracts of cells cultured on D-fructose-CA medium. These enzymatic activities were undetectable in extracts of cells grown in CA or succinate-CA medium. No decrease in the maximally induced specific activities of these enzymes occurred after the addition of succinate to cells during exponential growth on D-fructose-CA. Fructose 1,6-diphosphate aldolase and glucose-6-phosphate isomerase specific activities were approximately the same irrespective of cultural conditions. These results indicated that D-glucose was not utilized by cells of S. itersonii because this bacterium was impermeable to this hexose.