Cellulose is the most plentiful renewable biopolymer in nature which could be utilized by cellulolytic enzymes. Cellulases are among the most important groups of industrial enzymes which are widely consumed in biofuel production, pulp and paper, textile, and detergent industries. These enzymes can support a cleaner environment through reducing chemical processes in mentioned industries and agro-industrial waste management. Thermophilic filamentous fungi produce thermostable types of the enzymes with the property of hydrolysis the cellulose in higher temperatures with higher rates of reaction, decreased amounts of enzyme quantities and reduced risk of contamination by the mesophilic microorganisms. The cellulolytic capacity of two Thermoascus aurantiacus
isolates (from Mashhad, Iran) was examined in a simple liquid state fermentation in different carbon and nitrogen sources, in comparison to the Thermoascus aurantiacus
DSM 1831 as a reference fungus. Among different the tested sources, wheat bran and peptone led to the highest level of endoglucanase production by the isolated thermophilic fungi. The isolates showed higher cellulase activities, including endoglucanase, avicelase, and FPase, of the crude enzymes from the isolates in comparison to the reference fungus. Gene expression profiling revealed that changes in the cellulase mRNA levels are not correlated with the changes in protein activities during a 12-day period. This observation might be due to a complex process of enzymatic regulation of cellulases in response to the environmental signals.