Aims: To investigate the effects of temperature, pH, water activity (a w ) and CO 2 concentration on the growth of Rhizopus oligosporus NRRL 2710. Methods and Results: Hyphal extension rates from mycelial and spore inocula were measured on media with different a w ($ 1AE0, 0AE98 and 0AE96) and pH (3AE5, 5AE5 and 7AE5) incubated at 30, 37 or 42°C in atmospheres containing 0AE03, 12AE5 or 25% (v/v) CO 2 . The effects of environmental conditions on hyphal extension rate were modelled using surface response methodology. The rate of hyphal extension was very sensitive to pH, exhibiting a pronounced optimum at pH 5AE5-5AE8. The hyphal extension rate was less sensitive to temperature, a w or CO 2 , exhibiting maximum rates at 42°C, a w $ 1AE0 and 0AE03% (v/v) CO 2 . Conclusions: The fastest hyphal extension rate (1AE7 mm h )1 ) was predicted to occur at 42°C, pH 5AE85, a w $ 1AE0 and 0AE03% CO 2 .Significance and Impact of the Study: The present work is the first to model the simultaneous effects of temperature, pH, a w and CO 2 concentration on mould growth. The information relates to tempe fermentation and to possible control of the microflora in Tanzanian cassava heap fermentations.

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