Biosynthesis, purification and characterization of β-1,4-xylanase from a novel mangrove associated actinobacterium Streptomyces olivaceus (MSU3) and its applications

The present study was undertaken to evaluate the xylanolytic properties of an actinobacterium Streptomyces olivaceus (MSU3) isolated from the sediment sample of mangrove environment. It showed highest xylanase activity on initial screening in Breg's mineral salts medium supplemented with 0.5% xylan. Further the organism expressed maximum xylanase production at optimized culture conditions of pH 7, temperature 30 °C with 2.5% of inoculum size at 72 h of incubation, the nutrient sources like sucrose (2%) and yeast extract (3%) have observed as best carbon and nitrogen sources respectively. In purification, the xylanase resulted 4.27fold increase with the yield of 15.57% at the final step using sephadex G-75 chromatography. The molecular weight of the purified xylanase was observed as 42 kDa on 10% SDS-PAGE and further identified by MALDI-TOF-MS analysis. It belongs to GH43 family encoded 485 amino acid residues and the xylanase gene isolated using PCR amplification was partially sequenced. It showed 98% sequence similarity to the xylanase gene of S. olivaceus. The maximum activity of purified xylanase was observed at pH 8, temperature 40 °C and also the production medium substituted with Fe³⁺ metal ion, 2.0% xylan and 1.5% NaCl along with K_m and V_max values of 8.16 mg/ml and 250.01 μg/min/mg, respectively. In xylanolytic hydrolysis of pretreated agro-wastes, especially the sugarcane juice substituted medium yielded maximum (52.19%) reducing sugar, followed by bioethanol production (4.19 g/L) at 72 h of incubation. Based on the results, it could be confirmed that the selected isolate is a potent strain and it can able to produce xylanase through fermentation process and also it can able to convert the pretreated agro-wastes into economically important byproduct like bioethanol.