Inhibition of the tempe mould, Rhizopus oligosporus, by ammonia

The hyphal extension rate of Rhizopus oligosporus NRRL 2710 was slowed in the presence of 0·42 and 0·84 mmol NH3 l−1 and inhibited by 1·3 mmol l−1. Sporulation was prevented at NH3 concentrations of 0·42 mmol l−1 andabove. There was no evidence of toxicity due to NH+4 at concentrations up to 300 mmol l−1.Independent of the concentrations of NH3 or NH+4, the lower the pH value, in therange 6·0–9·0, the higher was the rate of hyphal extension. It is suggested that accumulationof toxic levels of NH3 could be responsible for the cessation of mould growth in tempe.