PRODUCTION AND PROCESSING OF A 59-KILODALTON EXOCHITINASE DURING GROWTH OF STREPTOMYCES-LIVIDANS CARRYING PCHIO12 IN SOIL MICROCOSMS AMENDED WITH CRAB OR FUNGAL CHITIN

Streptomyces lividans(pCHIO12), which carries the previously cloned St reptomyces olivaceoviridis exo-chiO1 gene on a multicopy vector, secre tes a 59-kDa exochitinase, consisting of a catalytic domain (40 kDa), a central fibronectin type III-like module, and a chitin-binding domai n (12 kDa), The propagation rate of S. lividans (pCHIO12) was higher i n soil microcosms amended with fungal mycelia than in those containing crab chitin. Comparative biochemical and immunological studies allowe d the following conclusions to be drawn. Within soil microcosm systems amended with crab shell chitin or chitin-containing Aspergillus proli ferans mycelia, the strain expressed the cloned exo-chiO1 gene and pro duced high quantities of a 59-kDa exochitinase, The enzyme was prefere ntially attached via its binding domain to the pellet from soil or liq uid cultures. In contrast, truncated forms of 47, 40, and 25 kDa could be easily extracted from soil. The relative proportions of the 59-kDa enzyme and its truncated forms varied depending on the source of chit in and differed in soil and in liquid cultures.