Ecology, toxicity, and hydrolytic activities of Bacillus thuringiensis in forests

Abstract

The investigation of Bacillus thuringiensis (Bt) in 16 forest soil samples from Ajloun, northern Jordan, involved the isolation of 23 isolates toxic to the third instar dipteran larvae of Drosophila melanogaster and 7 isolates toxic to the third instar lepidopteran larvae of Ephestia kuehniella. The highest viable count of Bt was found in Ebeen forest soils (14.24 × 10 7 CFU g-1), and the lowest viable count was found in Rasoun forest soils. The lethal concentration (LC50) of Bt isolates indicated a variation in their toxicity to D. melanogaster and E. kuehniella larvae, with lower LC50 values for D. melanogaster suggesting that D. melanogaster larvae are more susceptible to Bt toxins than E. kuehniella larvae. Serotyping of the 23 isolates toxic to D. melanogaster revealed that they belonged to 5 serotypes, including israelensis, kenyae, kurstaki, malaysiensis, and morrisoni. Serotype israelensis was the most dominant. The isolates toxic to E. kuehniella larvae belonged to serotype kurstaki and produced both bipyramidal and cuboidal parasporal crystals. It was observed that isolates producing toxic spherical parasporal crystals were the most abundant in the forest soils. Hydrolytic activities of Bt isolates recovered from forests were varied due to differences in their enzyme productivity. Most isolates had carboxymethylcellulase, amylase, lipase, and gelatinase activity, while pectinase activity was observed in only a few isolates. Maceration activity of the isolates to potato samples was more frequent than to carrot samples. The larvicidal and hydrolytic activities of tested Bt isolates demonstrated that a forest environment can be categorized as a rich source for Bt isolates that can be used in biological control and plant residue biodegradation. As a result, it is expected that Bt recovered from forests can be used to increase soil fertility and to enhance plant growth as well as productivity. © TÜBİTAK.