The relationship between insecticidal effects and chitinase activities of Coleopteran-originated entomopathogens and their chitinolytic profile

Abstract

Peritrophic membrane (PM) is present in most insects' midgut and acts as a mechanical barrier to protect the epithelium from various harmful factors such as pathogens or toxins. Chitinase is a virulence factor due to its ability to degrade the chitin content of PM. Therefore, chitinase is a mediator for easier binding of toxins to gut epithelium and intercepting nutritional absorption in the midgut. One hundred and eight bacterial isolates derived from microbial flora of coleopteran pests were screened to determine chitin-producing entomopathogenic bacteria. The M9 chitin-agar method and polymerase chain reaction with specific primers for a conserved domain of chitinase genes indicated that 23 of the 108 isolates have chitinase activity. The chitinase activities of the chitinase-positive bacteria were measured. We compared these results with the insecticidal activities results to determine, statistically, the potential relationship between the chitinase activities and the insecticidal activity. Consequently, 21.3% of bacterial isolates showed chitinolytic ability and among these the chitinase-positive bacteria, Serratia marcescens, was found the most active one in the M9-CAD method. More importantly, our study indicated a very strong positive correlation between the insecticidal activities of isolates and the chitinase activities with the M9-CAD method (r 2= 0.96, p≤0.01), but not with the DNS method (r 2=-0.279, p≤0.01). This strong relationship of entomopathogens has a high potential for biocontrol of Coleopteran pests. © Springer-Verlag and the University of Milan 2011.