Purification and Properties of a SDS-Resistant Xylanase from Halophilic Streptomonospora sp. YIM 90494

Lignocellulose, accounting for up to 30% of hemicellulose, plays an important role in producing cellulosic bioenergy. Xylan represents a large proportion of the hemicellulose in woody and graminaceous plant tissues and it is the second most abundant renewable polysaccharide in plant cell walls apart from cellulose. So far, xylanases have been isolated from different microorganisms, including Bacteria, Actinomycetes and Yeast.

Searching for xylanases from extremophilic microorganisms, such as acidophiles, alkaliphiles and thermophiles, have been studied widely. However, halophilic species have been addressed only to a very limited extent, only a few reports are available on xylanases from halophilic species.

This study firstly reported about xylanase from the halophilic Streptomonospora sp. YIM 90494 and special xylanase properties of the genus Streptomonospora. Meanwhile, the purification and iochemical properties of this enzyme were also studied in order to predict its possible industrial applications.

The results showed that the purified xylanase appeared as a single protein band on Sodium dodecyl sulfate-polycrylamide gel electrophoresis (SDS-PAGE) with a molecular mass of approximately 50 kDa. The xylanase had the maximum activity at pH 7.5 and 55°C. The enzyme was stable over a broad pH range (pH 4.0–10.0) and showed good thermal stability when being incubated at 60°C for 2 h.

Kinetic experiments indicated that the enzyme had Km and Vmax values of 19.24 mg/mL and 6.1 μmol/min/mg, respectively, using birch wood xylan as substrate. The inhibitory effects of various metal ions and chemical agents on the xylanase activity were investigated. It is greatly interesting to note that Ag⁺ ion and SDS, which strongly inhibited most xylanases reported previously increases the xylanase activity in this study.

These characteristics suggested that the enzyme with new properties has considerable potential in industrial applications. The result was published in Cellulose in August 2013.