Cyanide degradation by Rhizopus oryzae

Abstract

Rhizopus oryzae, a mucoraceous fungus associated with the postharvest spoilage of cassava was found to effectively metabolize cyanide. Degradation of cyanogenic glycosides of cassava by R. oryzae was studied by growing the organism in potato dextrose broth with and without linamarin and potassium cyanide. The influence of adaptation of the organism to low and high cyanide concentrations on both growth and the release of extracellular rhodanese into cyanide-containing media was studied. Nonadapted cultures of R. oryzae grow poorly when compared with the cyanide-adapted cultures. However non-adapted R. oryzae cultures released large quantities of rhodanese when compared with the adapted ones. Potassium cyanide (1.0 mM) was found to be an efficient inducer of rhodanese whereas potassium cyanide (5.0 mM) repressed the release of rhodanese. A significant inductive effect was produced by thiosulphate and thiocyanate. Linamarin repressed the rhodanese activity of cultures during the growth phase. Rhizopus oryzae also elaborated extracellular linamarase during its growth in broth with and without linamarin. This study revealed the potential use of R. oryzae in detoxifying the cyanogenic glycosides in cassava feed and food preparations as well as in the effective disposal of cyanide in industrial wastes.