Delineating thermophilic xylanase from Bacillus licheniformis DM5 towards its potential application in xylooligosaccharides production

In this present study novel endoxylanase producing Bacillus licheniformis DM5 isolated, identified based on 16S rDNA from Garampani hotspring, Assam, India and enzyme was purified. RNA secondary structure predicted the similarity of B. licheniformis DM5 with B. licheniformis ATCC14580. Highest production of xylanase from B. licheniformis DM5 was achieved in the TY medium with cell densities 12g/l and extracellular protein concentration containing xylanase 400mg/l. Partially purified extracellular xylanase displayed optimum pH 6.5 and temperature 50 degrees C. Thermostability of the xylanase at the elevated temperature showed stability between 50 and 60 degrees C retaining its 99% activity. Kinetic parameters of thermophilic xylanase revealed K-m 1.5 +/- 0.2mg/ml, V-max 2.7 +/- 0.2U/ml and and K-cat 1.8 +/- 0.2s(-1) against beechwood xylan but ruled out any exo-acting activity against synthetic pNP-xylopyranoside substrate. Time dependent enzymatic hydrolysis of beechwood xylan and preprocessed agrowaste corncob exhibited the release of xylotriose and xylobiose oligosaccharide (XOS) significantly high. Xylobiose and xylotriose exhibited higher binding affinities with BIAXP transporter protein of probiotic bacteria explaining their easy uptake by the cells. Mixed oligosaccharides also exhibited better prebiotic activity by promoting growth of Bifidobacterium infantis and Lactobacillus delbrueckii. Mixed XOS when tested for their cytotoxicity on Hela cell lines in in vitro MTT assay displayed significant lowering of cell viability after 48h and 24h at 100 mu g/ml to 60% and 50%, respectively. In contrast, cytotoxicity wasn't observed against normal cervical cell line (VK2/E6E7-ATCC-CRL-2616). Therefore, thermophilic endoxylanase from B. licheniformis DM5 could be attributed for the production of prebiotic and anti-inflammatory XOS from agrowaste.