A thermophile cellulase-producing bacterium was isolated and identified as closely related to Geobacillus subterraneus. The strain, named Geobacillus sp. T1. was able to grow and produce cellulase on cellobiose, microcrystalline cellulose, carboxymethylcellulose (CMC), barley straw, wheat straw and Whatman No. 1 filter paper. However, barley and wheat straws were significantly better substrates for cellulase production. When Geobacillus sp. T1 was cultivated in the presence of 0.5% barley straw, 0.1% Tween 80 and pH 6.5 at 50 degrees C. the maximum level of free cellulase up to 143.50 U/mL was produced after 24 h. This cellulase (similar to 54 kDa) was most active at pH 6.5 and 70 degrees C. The enzyme in citrate phosphate buffer (10 mM) was stable at 60 degrees C for at least 1 h. Geobacillus sp. T1 with efficient growth and cellulase production on straws seems a potential candidate for conversion of agricultural biomass to fuels. (c) 2012 Elsevier Ltd. All rights reserved.