Characterization and high-level production of xylanase from an indigenous cellulolytic bacterium Acinetobacter junii F6-02 from southern Taiwan soil

Hemicellulose, accounting for up to 30% of lignocellulose, could play an important role in producing cellulosic bioenergy. Xylanase is the key enzyme capable of hydrolyzing hemicellulose to form fermentable five-carbon sugars for biofuel production. A cellulolytic bacterial strain isolated from soil in southern Taiwan is able to produce xylanase and cellulase extracellularly with a high efficiency. The xylanase produced by the isolated strain (identified as Acinetobacter junii F6-02) exhibits the highest activity at 60 °C and pH 7.0. However, the best condition for producing xylanase by the F6-02 strain was 35 °C and pH 7.0 using BHM medium supplemented with CMC (5 g/L), xylan (5 g/L), and peptone (1 g/L). Fermentative production of xylanase was greatly influenced by oxygen supply, reaching the highest level at an aeration rate of 0.3 vvm. The highest cumulative xylanase production and xylanase production rate was 317 U/ml and 8.06 U/ml/h, respectively. The lyophilized cellulolytic enzymes produced from A. junii F6-02 display better enzyme activity than the original crude enzyme extract and are able to perform long-term hydrolysis stably at a temperature of 50 °C.