A 22 factorial design was performed to find the best pH and temperature for xylonolytic activity of cellulase-free Bacillus coagulans isolated from the Amazon environment. Solid-state cultivation was carried out on an inexpensive and abundant agro-industrial soybean residue. The central composite design (CCD) used for the analysis of treatment combinations showed that a second order polynomial regression model was in good agreement with experimental results, with R-2 = 0.8319 (P < 0.05). The maximum activity was obtained over a large range of temperatures (45-75 degreesC) and pH (4.5-10.0). Enzymic activity was maintained in heated extracts up to 50 degreesC, suggesting that the xylanases of B. coagulans are thermo-tolerant biocatalysts, being of interests for biobleaching processes. The crude enzyme extract hydrolyzed kraft pulp cellulose and its activity was stimulated by Co2+, Mn2+ and beta-mercaptoethanol but inhibited by Fe3+, Cu2+, Ca2+, Zn2+, Ba2+, Mg2+ and by EDTA. (C) 2003 Elsevier Ltd. All rights reserved.