Background and Objectivs: Trichophyton rubrum is considered as the most common causes of dermatophytosis in human skin and nail tissues. Microsporeum canis is a zoophile dermatophyte which can be transmited to human. HSP70 is a 70 KD heat shock protein in fungi. In this study, the effects of variable CO₂ concentrations were examined on HSP70 expression in T. rubrum and M. canis.
Materials and Methods: Strains used in this study were obtained from skin scales and nails of the patients who were suffering from onychomycosis. Samples were cultured on Sabouraud dextrose broth (SDB) and incubated at 25°C for 2, 4 and 7 days under 3%, 5%, and 10% of CO₂ concentrations. Control cultures maintained for 7 days without CO₂ concentrations. Then, RNA was isolated from the harvested mycelia mass, and HSP70 gene expression was studied in T. rubrum and M. canis by RT-PCR. The obtained results were compared to the Beta actin as a house keeping gene.
Results: The results of this study revealed the maximum variations under 3%,5%, and 10% of CO₂ concentrations in maximum 7 days incubation period, and the expression of HSP70 gene showed different  variations  under different CO₂ concentrations.
Conclusion: Our results showed a negative effect of CO₂ concentrations in the expression of HSP70 in T. Rubrum and a positive effect in M. canis comparing to the controls.