Abstract
Beauveria bassiana a natural soil borne insect pathogen is being used effectively these days in integrated pest management system. Foliar application of these fungi is quite satisfactory as it invades its host by adhering to insect cuticles through the formation of penetration structures called appresoria, which produces various extracellular enzymes, including chitinase that causes the insect cuticle breaching. Although many investigations have been done in this regard, only a little is known about the induction and repression mechanism of this hydrolytic enzyme. This report illustrates the effect of two carbon sources; colloidal chitin and dextrose and a nitrogen source, yeast extract on the chitinase production of seventeen B. bassiana isolates. The chitinase activity varied among the isolates and the different media studied. A high enzymatic activity was observed in the medium with colloidal chitin as a sole source of carbon followed by the medium containing an extra nitrogen source, yeast extract. Exochitinase activity and the chitinase activity gel were also determined for the isolates showing high chitinase enzyme activity. An array of chitinase isozymes were observed on chitinase activity gel with a common 70 kDa enzyme for all the isolates. Keywords: Beauveria bassiana, induction, colloidal chitin, chitinase, exochitinase.
Highlights
Chitin, the insoluble polymer of N-acetyl glucosamine (GlcNAc), is the second most abundant polymer in nature, generally found in insect cuticle
This report illustrates the effect of two carbon sources; colloidal chitin and dextrose and a nitrogen source, yeast extract on the chitinase production of seventeen B. bassiana isolates
Enzyme activity was investigated for a period of ten days and highest chitinase activity was observed between four to six days of culture
Summary
The insoluble polymer of N-acetyl glucosamine (GlcNAc), is the second most abundant polymer in nature, generally found in insect cuticle. It is quite difficult to chemically modify chitin (Muzzarelli, 1999) but it has been found that several microorganisms and plants and invertebrates have developed enzymatic systems that could metabolize this insoluble polymer. Microorganisms utilize chitin as a source of carbon. Plants employ this enzymatic system in defensive purposes and in the case of invertebrates, it is used during ecdysis period. Microorganisms, several insect pathogenic hyphomycete fungi produce hydrolytic enzymes that penetrate insect’s cuticle. The fungal conidia adhere to the cuticle surface through non specific hydrophobic interaction and produce penetration structure called appresoria which produces many cuticle hydrolytic enzymes
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