Family 19 chitinases of Streptomyces species: characterization and distribution.

Chitinase C from Streptomyces griseus HUT6037, described in 1997, is the first family 19 chitinase found in an organism other than higher plants. In this study, some properties of chitinase C were compared with those of family 18 bacterial chitinases, and the distribution of family 19 chitinases in Streptomyces species was investigated. The specific hydrolysing activity of chitinase C against soluble and insoluble chitinous substrates was markedly higher than those of bacterial family 18 chitinases. Chitinase C exhibited marked antifungal activity, whereas the other bacterial chitinases examined had no antifungal activity. Chitinase C was insensitive to allosamidin, whereas the family 18 bacterial chitinases were sensitive. Taking advantage of this insensitivity to allosamidin, a search was made for family 19 chitinases in various Streptomyces species. Chitinases insensitive to allosamidin were detected in the culture supernatants of all tested Streptomyces species. Southern hybridization analysis using a labelled DNA fragment corresponding to the catalytic domain of chitinase C strongly suggested that these species have genes similar to the chiC gene of S. griseus HUT6037. DNA fragments corresponding to the major part of the catalytic domains were amplified by PCR. The amplified fragments encoded amino acid sequences very similar to that of the corresponding region of chitinase C. Therefore, it was concluded that Streptomyces species generally possess family 19 chitinases which are very similar to chitinase C. Comparison of their amino acid sequences with those of plant family 19 chitinases revealed that Streptomyces family 19 chitinases are class IV type in terms of the presence and positions of deletions of amino acid sequences which are characteristic of plant class IV chitinases.