An alternative bacterial expression system using Bacillus pumilus SG2 chitinase promoter

Chitin is an abundant natural polysaccharide found in fungi, algae, and exoskeleton of insects. Several bacterial species are capable of utilizing chitin as their carbon source. These bacteria produce chitinases for degradation of chitin into N-acetyl-D-glucosamine. So far, regulation of the chitinase encoding genes has been studied in different bacterial species. Among Bacillus species, B. pumilus strain SG2 encodes two chitinases, ChiS and ChiL. The promoter region of chiSL genes (PchiS) is mainly regulated by the general carbon catabolite repression (CCR) system in B. subtilis due to the presence of a catabolite responsive element (cre). Use of PchiS in constructing an inducible expression system in B. subtilis was investigated. In the first step, complete and shortened versions of PchiS were inserted upstream of the lacZ on a pBS72/pUC18 shuttle plasmid. The b-galactosidase activity of B. subtilis carrying one of the relevant plasmids was measured in the presence of different carbon sources. An expression system based on the chitinase promoter of B. pumilus SG2 was established. Modification of PchiS and the culture medium resulted in production of b-galactosidase in B. subtilis up to 1,800 MU activity. The chitinase promoter developed in this study, has potential to be used in an expression vector that could be induced by chitin. In addition, compared to the other inducers like IPTG and lactose, chitin is definitely cheaper and more available as an inducer.