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

A 22 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 R2 = 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 Co2+, Fe3+, and β-mercaptoethanol but inhibited by Mn2+, Cu2+, Ca2+, Zn2+, Ba2+, Mg2+ and by EDTA.