Xylanase production from an alkalophilic actinomycete isolate Streptomyces sp. RCK-2010, its characterization and application in saccharification of second generation biomass

摘要

Xylanase production by a newly isolated Streptomyces sp. RCK-2010 was optimized for varying culture conditions following one factor at a time (OFAT) and response surface methodology (RSM) approaches. An initial medium pH 8.0, agitation 200 rpm, incubation temperature 40 C and inoculum size 1.0% (v/v) were found to be optimal for xylanase production (264.77 IU/ml), after 48 h of incubation. Among various carbon sources tested, the actinomycete secreted higher level of xylanase on wheat bran. The production medium when supplemented separately with various nitrogen sources, the enhanced xylanase production was observed with beef extract followed by peptone. RSM employing central composite design (CCD) was used to optimize the xylanase production using wheat bran, beef extract and peptone as model factors. The RSM showed that the optimum level of wheat bran (2.5% w/v), peptone (0.2% N2 equivalent) and beef extract (1.2% N2 equivalent) resulted in almost 3.0 fold improvement in xylanase production (2310.18 IU/ml). To the best of our knowledge this is the best xylanase volumetric productivity (1155 IU/ml/day) by any Streptomyces spp. reported in the literature. The enzyme was most active at 60 C and pH 6.0 and almost 40% stable after 4 h at optimum temperature. Saccharification of steam exploded rice straw with xylanase (60 IU/g dry substrate) supplemented with cellulase (24 FPU/g dry substrate) and β-glucosidase (60 IU/g dry substrate) resulted in 88% (w/w) saccharification of the cellulosic substrate.