Abstract:
Xylanase gene had been cloned from Streptomyces sp.42-9 through S. lividans TK64, a standard strain, in Streptomyces sp.190-1 by using a 5-Kb fragment of plasmid pIJ699 and plasmid pIJ702 as cloning vectors. S. lividans TK64 was used as an intermediate host cell for this gene cloning because it had approximately 100 folds higher transformation efficiency than that of Streptomyces sp.190-1. Three clones containing xylanase activity were obtained when a 5-Kb fragment from pIJ699 was used as a cloning vector. Recombinant plasmids pPT6C, pPT6E and pPT6G were isolated from these clones. Cultivation of S. lividans TK64 harboring pPT6C, pPT6E and pPT6G in a medium containing xylan yielded 5.19, 4.85 and 4.28 units of xylanase/ml of culture broth, respectively, while using Streptomyces sp.190-1 as a host yielded 2.93, 2.82 and 2.73 units of xylanase/ml, respectively. Size of the inserts in pPT6C, pPT6E and pPT6G were determined by agarose gel electrophoresis to be 4.8, 14.2 and 9.4 Kb, respectively. When pIJ702 was used as a cloning vector, five clones containing xylanase activity were obtained yielding five recombinant plasmids namely, pPT7-1, pPT7-2, pPT7-3, pPT7-4 and pPT7-5. Xylanase activity of S. lividans TK64 harboring pPT7-1, pPT7-2, pPT7-3, pPT7-4 and pPT7-5 when cultivated in xylan containing medium were 0.79, 0.73, 0.35, 0.32 unit/ml, respectively, but when Streptomyces sp.190-1 was used as a host for the corresponding plasmids 3.22, 3.13, 2.73, 1.92 and 2.32 units of xylanase/ml were produced, respectively. Size of the inserts in pPT7-1, pPT7-2, pPT7-3, pPT7-4 and pPT7-5 were determined to be 0.5, 4.4, 0.5, 6.4 and 4.4 Kb, respectively. Cloning of xylanase gene from Streptomyces sp.42-9 by using pIJ699 and pIJ702 as cloning vectors in Streptomyces sp.190-1 could increase xylanase producing ability of Streptomyces sp.190-1 to about 7-12 folds. Furthermore, Streptomyces sp.190-1 harboring plasmids containing xylanase gene were still able to produce about 800-1000 units of glucose isomerase per gram of dried cells.