Ninety bacteria isolated from raw composting materials were screened for their cellulolytic activity on solid medium containing carboxymethylcellulose. The bacteria producing the highest cellulolytic activity levels were identified by 16S rRNA sequencing as Bacillus licheniformis strain 1, Bacillus subtilis subsp. subtilis strain B7B, Bacillus subtilis subsp. spizizenii strain 6, and Bacillus amyloliquefaciens strain B31C. Cellulase activity production by the most productive strain B. amyloliquefaciens B31C was optimized in liquid culture varying the carbon source. Comparison of growth curves of B. amyloliquefaciens B31C at temperatures from 28 to 47 °C indicated its thermotolerant nature. Moreover, analysis of time courses of cellulase activity production in this thermal range showed that increase of temperature from 28 to 37 °C causes an increase of cellulase activity levels. Investigating the enzymes responsible for cellulase activity produced by B. amyloliquefaciens B31C by proteomic analyses, an endoglucanase was identified. It was shown that the purified enzyme catalyzes carboxymethylcellulose's hydrolysis following Michaelis–Menten kinetics with a KM of 9.95 mg ml−1 and a vmax of 284 μM min−1. It shows a retention of 90% of its activity for at least 144 h of incubation at 40 °C and exhibits a range of optimum temperatures from 50 to 70 °C.