Abstract

The present study describes the chitinolytic activity of extra cellular mosquitocidal proteins of Pseudomonas fluorescens and its involvement during pathogenesis in insects against larvae and pupae of Culex quinquefasciatus. The chitinolytic activity of purified extra cellular protein was assayed by using artificial colloidal chitin polymer substrates. The effect of purified protein in the alimentary canal and gut region of the treated larvae and pupae of C. quinquefasciatus was studied. The extra cellular protein of P. fluorescenswas found to exhibit chitinolytic activity and degraded the cuticular proteins in the treatedlarvae and pupae of C. quinquefasciatus. The Km and Vmax values toward pNP-(GlcNAC)₂ were 0.03 mM and 0.219 nmol/µg/min respectively. This result suggests that chitinolytic activity of extra cellular mosquitocidal protein of P. fluorescens play a critical role in chitin catabolism and was to weaken the insect’s chitinous structures/ peritrophic membranes. It leads to disruption of ionic regulation and death of the larvae or pupae treated with the proteins. It is concluded that chitinolytic activity is one of the reasons for the already reported mosquitocidal effect of the proteins of P. fluorescens.

Key words: Pseudomonas fluorescens, Culex quinquefasciatus, chitin, mosquitocidal protein, natural chitinase, larvae, pupae