Differential expression of actin modulated by temperature in mycelial and yeast cells of Paracoccidioides brasiliensis.

We used yeast and mycelial forms of Paracoccidioides brasiliensis to evaluate the effect of heat shock stress on actin expression. P. brasiliensis yeasts harvested during the exponential growth phase showed more expression of the actin mRNA when incubated at 40 degrees C than when incubated at 37 degrees C, the usual temperature at which these yeasts grow. In contrast, expression of actin mRNA was lower in yeasts incubated at 25 degrees C than in yeasts incubated at 37 degrees C. Mycelium harvested at 25 degrees C, an approximation of its normal growth temperature, and then exposed to 37 degrees C and 40 degrees C showed progressively higher expression of actin mRNA. Mycelial and yeast forms showed a similar pattern of response to exposure to supra-optimal temperatures: both showed the same increase in expression of actin. This suggests that actin may play a role not only in cellular differentiation but also in this species' rapid adaptive response to heat stress, a mechanism necessary to deal with a potentially hostile environment.