Properties of Streptomyces sp endo-β-xylanases in relation to their applicability in kraft pulp bleaching

A screening of a collection of Streptomyces sp. strains has shown that Streptomyces achromogenes 5028 (S1), Streptomyces longisporus ruber 4-167 (S2) and Streptomyces sp. 8812 (S3) degraded efficiently beechwood xylan. The beta-xylanase activities present in the culture filtrate of the strains were purified to electrophoretic homogeneity and found to be typical non-debranching endo-beta-xylanases (1,4-beta-D-xylan xylanohydrolases: E.C. 3.2.1.8) with respective molecular weights of 25,000 (S1), 45,000 (S2) and 22,000 (S3). The enzymes were characterized with respect to their temperature-pH relationship and kinetic profile. Immunological experiments suggested that the enzyme produced by S1 belonged to family 11 of glycanases and the S3 enzyme to family 10. The three xylanases adsorbed onto crystalline cellulose but were catalytically inert towards this material, indicating a possible application of these enzymes in biobleaching processes. With respect to its effect on kappa and brightness values in a DEDED bleaching sequence, the xylanase produced by the S1 strain appeared as comparable to a Trichoderma longibrachiatum commercial enzyme preparation (Novozym 431). Streptomyces sp. xylanases may find applications in elemental-chlorine-free bleaching procedures.