WATER RELATIONS OF SOME ZYGOMYCETES ISOLATED FROM FOOD

The water relations of six species from the Mucoraceae, Rhizopus stolonifer, R. oryzae, X. microsporus var. microsporus, Mucor circinelloides, Absidia corymbifera and Syncephalastrum racemosum were studied at 25 degrees C and 30 degrees over a water activity (a(w)) range of 0.995 to 0.80 in glucose-based media. Three isolates of each species were used in a mixed inoculum to minimize isolate to isolate variation. Germination or growth was apparent in all species in less than 12 h from 0.995 to 0.96 a(w). At 0.84 a(w), R. stolonifer germinated in less than 3 d. R. stolonifer and R. oryzae grew very rapidly (1.5-2.0 mm h(-1)) at the highest a(w), but the growth rate fell as a(w) was decreased. R. stolonifer and S. racemosum, the most xerophilic of the fungi studied, were able to grow at 0.84 a(w). The minimum a(w), for growth of R. oryzae and A. corymbifera was 0.88 a(w), while the lowest a(w) for growth of R. microsporus var. microsporus and M. circinelloides was 0.90 a(w). Growth rates were generally slightly faster at 30 degrees than at 25 degrees, but water relations of most species were similar at both temperatures.