The Physiology of Riboflavin Production by Eremothecium ashbyi

SUMMARY During the submerged batch cultivation of a riboflavin-producing strain of Eremothecium ashbyi three phases were observed. The first phase was characterized by rapid growth of mycelium, rapid utilization and oxidation of glucose and a decrease of pH value caused by accumulation of pyruvic acid. Subsequently acetoin accumulated in the medium. Glucose was oxidized incompletely since only 1 -8 pmole oxygen were consumed/pmole glucose utilized. The end of this phase was marked by exhaustion of glucose and cessation of growth. The second phase began with sporulation and was characterized by rapid synthesis of cell-bound riboflavin. Simultaneously a rapid increase in catalase activity and decreases of pyruvate and acetoin were observed. This was accompanied by a marked decrease in Qo, on glucose while the Qo, on pyruvate, threonine or acetaldehyde increased to a maximum. Ammonia accumulated in the medium and alkaline pH values were reached. The third phase was characterized by autolysis of mycelium which led to the release of riboflavin and to a decrease of enzymic activities. A comparison of all important physiological parameters was made with two strains of E. ashbyi of different riboflavin productivity. On the basis of correlation between riboflavin formation, catalase activity and respiration on acetaldehyde, an hypothesis is proposed to explain overproduction of riboflavin by a shift from the initial cytochrome type of terminal respiration to the flavoprotein type which is, however, accompanied by over-production of the flavin prosthetic group.