Involvement of chitinases of Bacillus thuringiensis during pathogenesis in insects

• Published in: Microbiology (Society for General Microbiology) Vol. 144; no. 8; pp. 2189 - 2194
• Main Authors: Sampson, Mark N, Gooday, Graham W
• Format: Journal Article
• Language: English
• Published: Reading Soc General Microbiol 01.08.1998; Society for General Microbiology
• Subjects: Acetylglucosamine - analogs & derivatives; Acetylglucosamine - pharmacology; Animals; Bacillus thuringiensis; Bacillus thuringiensis - drug effects; Bacillus thuringiensis - enzymology; Bacillus thuringiensis - pathogenicity; Bacteriology; Biological and medical sciences; Chironomidae - drug effects; Chironomidae - growth & development; Chironomidae - microbiology; Chitinases - antagonists & inhibitors; Chitinases - pharmacology; Chitinases - physiology; Culicoides nubeculosus; Fundamental and applied biological sciences. Psychology; Larva - drug effects; Larva - growth & development; Larva - microbiology; Microbiology; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Pest Control, Biological; Spodoptera - drug effects; Spodoptera - growth & development; Spodoptera - microbiology; Trisaccharides - pharmacology; Chitinase; Entomopathogen; Enzyme; Insecta; Bacillus thuringiensis; Host agent relation; Bacillaceae; Spodoptera littoralis; Pathogenicity; Bacillales; Arthropoda; Glycosidases; Lepidoptera; Bacteria; Hydrolases; Noctuidae; Invertebrata; O-Glycosidases; Microbial insecticide
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/00221287-144-8-2189

Department of Molecular and Cell Biology, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK ABSTRACT Bacillus thuringiensis subsp. israelensis IPS78 and B. thuringiensis subsp . aizawai HD133 both secreted exochitinase activity when grown in a medium containing chitin. Allosamidin, a specific chitinase inhibitor, inhibited activity from both strains, with IC 50 values of about 50 µM with colloidal chitin as substrate and between 1 and 10 µM with 4-methylumbelliferyl-diacetylchitobioside and 4-methylumbelliferyl-triacetylchitotrioside as substrates. The involvement of these chitinolytic activities during pathogenesis in insects has been investigated with B. thuringiensis subsp. israelensis IPS78 against larvae of the midge Culicoides nubeculosus , and with B. thuringiensis subsp. aizawai HD133 against caterpillars of the cotton leafworm Spodoptera littoralis . Presence of 100 µM allosamidin increased the LD 50 by factors of 1.3 and 1.4, respectively, demonstrating a role for bacterial chitinases in the attack on the insects. Presence of chitinase A from Serratia marcescens considerably decreased the values for LD 50 ' confirming previous observations with different systems of the potentiation of entomopathogenesis of B. thuringiensis by exogenous chitinases. The most likely action of the endogenous chitinases of B. thuringiensis is to weaken the insects' peritrophic membranes, allowing more ready access of the bacterial toxins to the gut epithelia. Addition of exogenous chitinases will then increase this effect. Complementary cross-infection experiments, strain HD133 against midge larvae and strain IPS78 against caterpillars, were performed to investigate the pathogen/host specificities of the effects. Results showed that much higher concentrations of bacteria were required to achieve even low mortalities, and addition of chitinase A gave no increase in death rate. * Author for correspondence: Graham W. Gooday. Tel: +44 1224 273147. Fax: +44 1224 273144. e-mail: g.w.gooday@abdn.ac.uk Keywords: chitinase, peritrophic membrane, Bacillus thuringiensis toxin, allosamidin, entomopathogenesis Present address: Warwick International Group Ltd, Mostyn, Holywell, Flintshire CH8 9HE, UK.