Chitinolytic proteins secreted by Cellulosimicrobium sp. NTK2

Abstract

ABSTRACT Cellulosimicrobium sp. NTK2 (NTK2 strain) was isolated as a chitinolytic bacterium from mature compost derived from chitinous waste. The growth of the NTK2 strain was enhanced by supplementation of the culture medium with 2% crystalline chitin. Approximately 70% of the supplemented crystalline chitin was degraded during cultivation. Whole genome analysis of the NTK2 strain identified eight chitinases and two chitin-binding proteins. The NTK2 strain secreted two bacterial extracellular solute-binding proteins, three family 18 glycosyl hydrolases and one lytic polysaccharide monooxygenase specifically in the presence of crystalline chitin. A chitinolytic enzyme with a molecular mass of 29 kDa on SDS-PAGE under native conditions was also secreted. This chitinolytic enzyme exhibited the largest band upon zymography but could not be identified. In an attempt to identify all the chitinases secreted by the NTK2 strain, we expressed recombinant versions of the proteins exhibiting chitinolytic activity in Escherichia coli. Our results suggest that the 29 kDa protein belonging to family 19 glycosyl hydrolase was expressed specifically in the presence of 2% crystalline chitin.