Involvement of chitinases of Bacillus thuringiensis during pathogenesis in insects

Abstract

Bacillus thuringiensis su bsp. israelensis IPS78 and B. thuringiensis su bsp. aizawai HD133 both secreted exochitinase activity when grown in a medium containing chitin. Allosamidin, a specific chitinase inhibitor, inhibited activity from both strains, with I C, values of about 50 pM with colloidal chitin as substrate and between 1 and 10 pM with 4-methylumbelliferyldiacetylchitobioside 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 pM allosamidin increased the LD50 by factors of 1.3 and 14, 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,, 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 pathogenhost 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.

Specificity determinants for Cry insecticidal proteins: Insights from their mode of action

“…Similarly, pretreatment with GalNAc was shown to reduce Cry1Ac sequestration to the peritrophic matrix and increase susceptibility in Bombyx mori larvae (Hayakawa et al, 2004). Reduced activity of Bt strains in the presence of chitinase inhibitors (Ding et al, 2008;Lertcanawanichakul et al, 2004;Regev et al, 1996;Sampson and Gooday, 1998), further supports that the ability to evade the peritrophic matrix may greatly contribute to determine specificity. The specific composition of the peritrophic matrix in distinct insects, especially in terms of protein glycosylation, would be expected to have a relevant impact on its effect on Bt toxin specificity.…”

Insect pathogenicity in plant-beneficial pseudomonads: phylogenetic distribution and comparative genomics

“…israelensis IPS68 and B. thuringiensis subsp. aizawai HD133 were shown to contribute to insecticidal activity toward Culicuoides nubeculosus and S. littoralis, respectively (Sampson and Gooday, 1998). In insecticidal strains of the P. fluorescens group, we identified two chitinase genes.…”

High-efficient synthesis and biological activities of allosamidins

“…Compound 1 and its derivatives, namely, demethylallosamidin, methylallosamidin, glucoallosamidin A, glucoallosamidin B and methyl-N-demethylallosamidin 37 , were also tested against different human pests and pathogens such as plasmodium 38,39 and nematodes 40 . Allosamidin 1 also possesses antibacterial 41 and antifungal activities against the pathogenic fungi 42 . In Streptomyces species that produce compound 1, this inhibitor favours production of an allosamidininsensitive chitinase, which is necessary for fungi growth 43 .…”