Aromatic metabolism in the fungi. Growth of Rhodotorula mucilaginosa in p-hydroxybenzoate-limited chemostats and the effects of growth rate on the synthesis of enzymes of the 3-oxoadipate pathway.

Rhodotorula mucilaginosa was grown in p-hydroxybenzoate-limited chemostats over the dilution rate (D) range 0.01 to 0.17 h-1 and growth was adequately described by the Monod theory when maintenance energy requirements were considered. The p-hydroxy-benzoate affinity constant, K8, had the relatively high value of 270 mg/I. The yield from p-hydroxbenzoate varied with dilution rate but was constant above D equal 0.07 h-1 at 0.56 g yeast/g substrate utilised. The maintenance coefficeint for growth on the aromatic substrate was 20 mg/g yeast/hr. Culture viability decreased linearly as the dilution rate was reduced. 4-Hydroxybenzoate 3-mono-oxygenase, protocatechuate 3,4-dioxygenases, 3-carboxymuconate cyclase and 3-carboxymuconolactone hydrolase activities were dilution rate-dependent, results which accord with the substrate in inducibility of these enzymes. Under carbon-limited growth conditions the addition of glucose, a catabolite repressor of these enzymes, to the aromatic medium stimulated their synthesis. Data were also obtained which indicated that whereas the synthesis of the cyclase and the hydrolase was coordinately controlled, that of the first two enzymes of the 3-oxodipate pathway was under independent control.