Screening of a Soil Bacteria Collection for the Production of Alkali Thermostable Xylanases

This work aimed to evaluate a collection of common and rare soil bacteria regarding to extracellular xylanases production and to characterize the stability in contrasting conditions of temperature and pH of these enzymes. This collection consists of 120 isolates belonging to six phyla that were subjected to screening for xylanase activity in pure cultures and in the extracellular proteic extract (EPE). The ratio between the halos diameters of xylan hydrolysis and in the colonies on solid medium (ratio H-C) was used for the evaluation of cultures as selection criteria. EPEs of isolates with highest ratios H-C were evaluated for the specific xylanases activity at 50 °C for 1 h. EPE of the three isolates with the highest potential for activity under this condition were evaluated for optimum activity, stability at 60 °C and different pH values. Twenty-two isolates showed xylanase activity under these conditions. Xylanases from TC21 and TC119 showed high relative activity at temperatures up to 70 °C and were less sensitive to changes in pH. Soil bacteria show high potential as a source of extracellular xylanases adapted to extreme pH and temperature conditions, which are required in agroindustrial processes.