subsp. IPS78 and . HD133 both secreted exochitinase activity when grown in a medium containing chitin. Allosamidin, a specific chitinase inhibitor, inhibited activity from both strains, with IC 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 subsp. IPS78 against larvae of the midge , and with subsp. HD133 against caterpillars of the cotton leafworm . Presence of 100 μM allosamidin increased the LD 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 considerably decreased the values for LD' confirming previous observations with different systems of the potentiation of entomopathogenesis of by exogenous chitinases. The most likely action of the endogenous chitinases of 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.


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