Cloning, sequence analysis, and expression of genes encoding Xylan-degrading enzymes from the thermophile 'Caldocellum saccharolyticum'

Abstract

A λ recombinant bacteriophage coding for xylanase and β-xylosidase activity has been isolated from a genomic library of the extremely thermophilic anaerobe 'Caldocellum saccharolyticum'. Partial Sau3AI fragments of the λ recombinant DNA were ligated into pBR322. A recombinant plasmid with an insertion of ca. 7 kilobases of thermophilic DNA expressing both enzymatic activities was isolated. The location of the genes has been established by analyzing deletion derivatives, and the DNA sequence of 6.067 kilobases of the insert has been determined. Five open reading frames (ORFs) were found, one of which (ORF1; M(r) 40,455) appears to code for a xylanase (XynA) which also acts on o-nitrophenyl-β-D-xylopyranoside. Another, ORF5 (M(r) 56,365), codes for a β-xylosidase (XynB). The xynA gene product shows significant homology with the xylanases from the alkalophilic Bacillus sp. strain C125 and Clostridium thermocellum.