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

The objectives were to determine the influence of water activity (a(w), 0.997-0.92) and temperature (10-37°C) and their interactions on conidial germination, mycelial growth and sporulation of two strains of Stachybotrys chartarum in vitro on a potato dextrose medium. Studies were carried out by modifying the medium with glycerol and either spread plating with conidia to evaluate germination and germ tube extension or centrally inoculating treatment media for measuring mycelial growth rates and harvesting whole colonies for determining sporulation. Overall, germination of conidia was significantly influenced by a(w) and temperature and was fastest at 0.997-0.98 a(w) between 15 and 30°C with complete germination within 24 h. Germ tube extension was found to be most rapid at similar a(w) levels and 25-30°C. Mycelial growth rates of both strains were optimal at 0.997 a(w) between 25 and 30°C, with very little growth at 37°C. Sporulation was optimum at 30°C at 0.997 a(w). However, under drier conditions, this was optimum at 25°C. This shows that there are differences in the ranges of a(w) x temperature for germination and growth and for sporulation. This may help in understanding the role of this fungal species in damp buildings and conditions under which immune-compromised patients may be at risk when exposed to such contaminants in the indoor air environment.