Characterization of chitinase-producing Serratia and Bacillus strains isolated from insects

Abstract

Chitinases (EC 3.2.1.14) are enzymes that hydrolyze chitin by cleaving beta-1,4 N-glycosidic bonds. These enzymes have been used for multiple applications in biotechnology, especially for controlling insect pests and phytopathogenic fungi. In the present study, we isolated two chitinase-producing bacteria strains from insects (strain SCH-1 from Moechotypa diphysis and strain SCH-2 from Sphedanolestes impressicollis). Serratia sp. SCH-1 was a short, rod-shaped facultative anaerobe, while Bacillus strain SCH-2 was a rod-shaped endospore-forming anaerobe. Strains SCH-1 and SCH-2 were identified as Serratia sp. and Bacillus sp., respectively based on 16S rRNA gene sequencing. Strain SCH-1 shared maximum homology (99.44%) with Serratia nematodiphila DZ0503SBS1 and Serratia marcescens subsp. sakuensis KRED. Strain SCH-2 had a maximum homology of 99.24% with Bacillus thuringiensis ATCC 10792 and Bacillus toyonensis BCT-7112. Serratia sp. SCH-1 contained greater levels of saturated fatty acids, but the concentration of branched acids, especially iso-C-15:0, was highest in Bacillus sp. SCH-2. Serratia sp. SCH-1 possessed chitinase activity of 1.59 unit/mg protein after 5 days of incubation in culture medium. In contrast, Bacillus sp. SCH-2 had a maximum activity of 0.84 unit/mg protein after 4 days of incubation. Chitinase isozymes produced by Serratia sp. SCH-1 appeared as five bands with sizes of 20, 26, 36, 45 and 54 kDa. Bacillus sp. SCH-2 showed a chitinase isozyme profile with three bands having sizes of 36, 45 and 50 kDa on SDS-PAGE gels.