Extracellular rhodanese production by Rhizopus oryzae

Rhizopus oryzae , associated with the post-harvest spoilage of cassava, produced high levels of extracellular rhodanese during exponential phase of growth. The fungus could grow and yield more rhodanese at pH 4.6-5.4 and temperature 30-35 degree C; however, the optimum assay conditions of the enzyme was found to be at a temperature of 40 degree C and pH 6.0. Glucose or other low molecular weight metabolizable sugars did not repress the synthesis of rhodanese, indicating the lack of catabolite repression in this organism. Of the nitrogen sources examined, peptone, yeast extract and nitrate salts enhanced the yield of rhodanese. The addition of surfactants, such as Tween 80 at 0.1% level to fungal culture media markedly increased rhodanese production. Potassium cyanide (KCN) at 0.25 and 0.5 mM levels was found to induce rhodanese synthesis; beyond these levels, it completely suppressed the cell growth.