Inhibition of the tempe mould, Rhizopus oligosporus, by ammonia

The hyphal extension rate of Rhizopus oligosporus NRRL 2710 was slowed in t he presence of 0.42 and 0.84 mmol NH(3)1(-1) and inhibited by 1.3 mmol l(-1 ). Sporulation was prevented at NH3 concentrations of 0.42 mmol l(-1) and a bove. There was no evidence of toxicity due to NH: at concentrations up to 300 mmol l(-1) Independent of the concentrations of NH3 or NH4+, the lower the pH value, in the range 6.0-9.0, the higher was the rate of hyphal exten sion. It is suggested that accumulation of toxic levels of NH, could be res ponsible for the cessation of mould growth in tempe.