Production and partial characterisation of xylanase from Streptomyces sp. strain AMT-3 isolated from Brazilian cerrado soil

Streptomyces sp. AMT-3 strain previously isolated from Brazilian cerrado soil has been selected as a promising strain for xylanase production. This bacterial strain was able to produce a medium–high range of extracellular xylanolytic activity levels for liquid cultures containing commercial xylans (birchwood, larchwood and oat spelts) and agro-industrial by-products and wastes. Although the best xylanase production (70.0 U ml −1) was obtained in growth medium containing larchwood xylan 1% (w/v), xylanolytic activity was also observed when wheat bran (28.4 U ml −1), wheat germ (20.4 U ml −1), brewer’s spent grain (16.0 U ml −1), corn cobs (9.1 U ml −1) and paper recycling mill sludge (7.9 U ml −1) were used as substrates. The Streptomyces sp. AMT-3 strain xylanase activity was characterised in terms of temperature and pH profiles and thermostability. Best enzyme activity was observed at the temperature range from 55 to 65 °C and at pH 6.0. The enzyme retained 50% of its activity after 20 h at 55 °C. As such, this xylanase could be considered as a thermotolerant biocatalyst being interesting for biotechnological applications. Zymogram analysis of the culture supernatant indicated the presence of several bands suggesting the presence of isoenzymes with different molecular weights. When cells were grown on agro-industrial by-products lower molecular weight bands were more evident.