Isolation and Characterization of Bacillus thuringiensis Berliner from Soil, Leaf, Seed Dust and Insect Cadaver

Abstract

Improved methods of isolation of Bacillus thuringiensis (Bt) has resulted in the isolation of novel strains with new host range, increased toxicity over the existing isolates and as source of isolation of novel genes. The potent and novel genes of Bt such as vegetative inseeticidal proteins (Vip) and binary toxins are currently used for production of insect resistant transgenic plants. In the present investigation Bt has been isolated from the following sources viz., soil (19 out of 38 locations), leaf (one out of 12 samples), seed dust (two out of seven samples) and insect cadavers (two out of nine insect species). Average population of the Bt isolates varied from 0.24 í— 10³ cfu/g in soil; 0,04 cfu/cm² in leaf; 0.09 í— 10² cfu/g in seed dust and 1.38 í— 10⁵ cfu/larva in insect cadaver. As far as the number of Bt isolates obtained from different sources 28, one, two and two isolates were obtained from soil, leaf, seed dust&insect cadaver, respectively. Out of the total 33 isolates 18, 10 and five isolates produced bipyramidal, rhomboidal and spherical crystals, respectively. Preliminary toxicity studies showed that the 18 isolates that produced bipyramidal crystals were toxic to the five-day-old larvae of Plutella xylostella (Linnaeus). PCR screening of the above isolates using hemolysin specific primers showed that the objectionable exotoxin, hemolysin was present in only one isolate, DVu-1 obtained from the seed dust of Vigna unguiculata (Linnaeus).