초록
Microbial xylanases have attracted much attention because of their applications in industrial processes during the past few decades. Sixty-five terrestrial actinomycetes previously isolated from rhizospheric soils of endemic plants were tested for their ability in production of xylanase. The results revealed that 33 isolates could degrade xylan on both solid and liquid media. Extracellular xylanase production by these isolates was characterized during their growth in liquid medium. Streptomyces sp. CA24, one of the most active strains, was selected for optimization of xylanase production. The enzyme secretion was enhanced when the medium was supplemented with oat spelt xylan (0.5%) and yeast extract (0.5%) at pH 10.0. Optimization of the culture conditions resulted in a 5-fold enhancement in enzyme production (255 U/mL). The most important characteristic of the enzyme is its production over a broad pH range of 6.0-10.0 during all stationary phases. The cellulase-free xylanase was optimally active at 60 °C and almost 90% stable after 4 h at 50 °C. The high levels of enzyme production obtained under alkali batch cultivation conditions, coupled with no production of cellulase, suggests the use of the local terrestrial strain Streptomyces CA24 and/or its enzyme in industrial processes such as pulp and paper production.