Statistical optimization of thermo-tolerant xylanase activity from Amazon isolated Bacillus circulans on solid-state cultivation

A 2 2 factorial design was performed to find the best conditions of pH and temperature for xylanolytic activity of Bacillus circulans BL53 isolated from the Amazon environment. Solid-state cultivation was carried out on an inexpensive, 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 = 0.9369 ( P < 0.05). The maximum activity was obtained at a high temperature (80 °C) and over a large pH range (4.0–7.0). Enzymatic activity was maintained in heated extracts up to 50 °C, suggesting that the xylanases of B. circulans BL53 are thermo-tolerant biocatalysts, being of interest for industrial processes. The crude enzyme extract hydrolyzed rice straw, sugar cane bagasse and soybean fiber and its activity was stimulated by Co 2+, Fe 3+, and β-mercaptoethanol but inhibited by Mn 2+, Cu 2+, Ca 2+, Zn 2+, Ba 2+, Mg 2+ and by EDTA.