The influence of water activity and temperature on germination, growth and sporulation of stachybotrys chartarum strains

The objectives were to determine theinfluence of water activity (aw, 0.997-0.92) andtemperature (10-37C) and their interactions onconidial germination, mycelial growth and sporulationof two strains of Stachybotrys chartarum in vitroon a potato dextrose medium. Studies were carriedout by modifying the medium with glycerol andeither spread plating with conidia to evaluate germinationand germ tube extension or centrally inoculatingtreatment media for measuring mycelialgrowth rates and harvesting whole colonies fordetermining sporulation. Overall, germination ofconidia was significantly influenced by aw andtemperature and was fastest at 0.997-0.98 aw between15 and 30C with complete germination within 24 h.Germ tube extension was found to be most rapid atsimilar aw levels and 25-30C. Mycelial growth ratesof both strains were optimal at 0.997 aw between 25and 30C, with very little growth at 37C. Sporulationwas optimum at 30C at 0.997 aw. However,under drier conditions, this was optimum at 25C.This shows that there are differences in the ranges ofaw x temperature for germination and growth and forsporulation. This may help in understanding the roleof this fungal species in damp buildings and conditionsunder which immune-compromised patientsmay be at risk when exposed to such contaminantsin the indoor air environment.