Isolation and characterization of native Bacillus thuringiensis isolates from Syrian soil and testing of their insecticidal activities against some insect pests

Abstract

Bacillus thuringiensis was detected in 12.5% of soil samples collected from different regions in Syria and 25 B. thuringiensis isolates were found to be highly toxic to larvae of Ephestia kuehniella Zeller, Phthorimaea operculella Zeller, and Cydia pomonella L. (Lepidoptera), but not to the larvae of Culex quinquefasciatus (Diptera). Light microscopy investigation showed the presence of bipyramidal and cuboidal parasporal bodies produced by these isolates. The existence of different cry genes in the tested isolates was studied using a PCR strategy with a set of general primers recognizing some of the cry genes reported in the relevant literature. Primers corresponding to 2 types of cry genes (cry1 and cry2) successfully amplified DNA in all of the tested isolates. Moreover, the proteins encoded by these genes were detected in the SDS-PAGE of the purified parasporal bodies. The 50% lethal concentration of the spore-crystal mixture of the 25 isolates against E. kuehniella larvae varied from 8.4 to 97.6 µg g^{-1}. A comparison of the LC_{50} values of the tested isolates with those of the reference strains B. thuringiensis kurstaki HD-1 and HD-73 (20.8 and 46 µg g^{-1}, respectively) showed that some of these isolates have a higher toxicity potential. Moreover, flagellar serotyping revealed that 4 isolates, which were among the most toxic, belonged to serotype kurstaki. This study constitutes the first isolation and characterization of local B. thuringiensis isolates in Syria. Some of these isolates exhibit toxic potential and, therefore, could be adopted for future applications to control some important insect pests.