Method for the rapid screening of cellulolytic streptomycetes and their mutants

Beta-mannanase of Streptomyces lividans 66: cloning and DNA sequence of the manA gene and characterization of the enzyme

The gene coding for a beta-mannanase was cloned homologously from Streptomyces lividans and its DNA sequence was determined. The fully secreted enzyme was isolated and purified from culture filtrates of the hyperproducing clone S. lividans IAF36 grown in mineral salt media containing galactomannan as the main carbon source. It had a molecular mass of 36 kDa and a specific activity of 876 i.u./mg of protein. Under the assay conditions used, the optimal enzyme activity was obtained at 58 degrees C and a pH of 6.8. The pI was 3.5. The kinetic constants of this mannanase determined with galactomannan as substrate were a Vmax. of 205 i.u./mg of enzyme and a Km of 0.77 mg/ml. Data from SDS/PAGE and Western blotting show that the cloned enzyme was identical to that of the wild-type strain.

Cloning of a second xylanase-encoding gene of Streptomyces lividans 66

A second xylanase-encoding gene (xln) of Streptomyces lividans 66 was cloned by functional complementation of a xylanase/endocellulase-negative double mutant of S. lividans, using the multicopy plasmid pIJ702. Three clones contained a common 3.1-kb DNA fragment encoding the biosynthesis of a 31-kDa xylanase and a 22-kDa protein which was immunorelated. The xylanase represented at least 80% of the total secreted proteins. These three clones also secreted a small amount of the previously reported 43-kDa xylanase which was detected only by using specific antibodies. Most likely, the DNA fragment contained the complete structural xln gene and some regulatory sequences, since the enzymatic activity was repressed by glucose. In the in vitro transcription-translation system, the plasmid pIAF42 encoded an immunoprecipitable 35-kDa xylanase indicating the presence of a 4-kDa signal peptide.