PHYSIOLOGY OF GLUCONABACTER-OXYDANS DURING DIHYDROXYACETONE PRODUCTION FROM GLYCEROL

Investigations into physiological aspects of glycerol conversion to di hydroxyacetone (DHA) by Gluconobacter oxydans ATCC 621 were made. The activity levels of the enzymes involved in the three catabolic pathway s previously known and the effects of specific inhibitors and uncoupli ng agents on cellular development, DHA synthesis, and cellular respira tory activity were determined. It was established that only two catabo lic pathways are involved in glycerol dissimilation by this micro-orga nism. The only enzyme responsible for DHA production is membrane-bound glycerol dehydrogenase, which employs oxygen as the final acceptor of reduced equivalents without NADH mediation. The ketone is directly re leased into the culture broth. As the glycolytic and carboxylic acid p athways are absent, the pathway provided by the membrane-bound enzyme is indispensable for the energy requirements of G. oxydans. The cytopl asmic pathway, which begins by phosphorylation of glycerol followed by a dehydrogenation to dihydroxyacetone phosphate, allows growth of the bacterium. At the same time, the substrate transport mode was charact erized as facilitated diffusion using radioactive [1(3)-H-3]-glycerol. Concerning the DHA inhibition of microbial activity, the enzymatic st udy of the membrane-bound glycerol dehydrogenase showed the enzymatic origin of this phenomenon: a 50% decrease of the enzyme activity was o bserved in the presence of 576 mM DHA. The decrease in the rate of pen etration of glycerol into cells in the presence of DHA indicates that growth inhibition is essentially due to the high inhibition exerted by the ketone on the substrate transport system.