Chitinase System in Streptomyces.

The ability to hydrolyze chitin to utilize as a carbon source is an important characteristic of Streptomyces, which are considered to be major decomposers of chitin in soil. Chitinase genes have been cloned from Streptomyces species. Extensive analysis of these genes revealed an extraordinary high multiplicity of chitinase genes in Streptomyces. In S. coelicolor A3(2), seven distinct genes belonging to family 18 and 19 chitinases were dispersed on the chromosomal DNA. Such high-multiplicity of chitinase genes was observed in the wide range of species of Streptomyces. Genes for family 19 chitinases, which had been considered to be present only in higher plants, were found to be widely spread in Streptomyces. Proteolytic-cleavage of primary gene products also contribute to the high-multiplicity of chitinases produced by Streptomyces. Many of Streptomyces chitinases, especially those of family 18, have multiple domain structure consisting of substrate- binding domain, fibronectin type III-like domain, and catalytic domain. Chitinase synthesis in Streptomyces is induced by chitin and repressed by the presence of readily utilizable carbon sources such as glucose. The regulation of chitinase synthesis is carried out at the level of transcription. Present in the promoter region of almost all the chitinase genes of Streptomyces is a pair of 12-bp-direct repeat sequences, which was shown to be involved in the regulation of chitinase genes transcription. In glucose repression of chitinase production, glkA, a gene for glucose kinase, is involved in S. lividans, but apparently not in S. coelicolor A3(2).