WATER RELATIONS OF SOME ZYGOMYCETES ISOLATED FROM FOOD

The water relations of six species from the Mucoraceae, Rhizopus stolo nifer, R. oryzae, X. microsporus var. microsporus, Mucor circinelloide s, Absidia corymbifera and Syncephalastrum racemosum were studied at 2 5 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 u sed in a mixed inoculum to minimize isolate to isolate variation. Germ ination 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 studi ed, 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 gr owth 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 bot h temperatures.