A new Tunisian strain of Bacillus thuringiensis kurstaki having high insecticidal activity and δ-endotoxin yield

Abstract

BLB1 is a new Bacillus thuringiensis kurstaki strain, isolated from a Tunisian soil sample. Assay of toxicity of BLB1 crystal proteins resulted in an LC50 of 70.32 ng of toxin per mg of flour against third instar Ephestia kuehniella with confidence limits of (31.6-109.04 ng). This LC50 is less than that of the commercial strains HD1 used as a reference. The characterization of this strain by scanning transmission electron microscopy, analysis of its cry genes content by PCR-sequencing, and analysis of its delta-endotoxin patterns demonstrate that it belongs to the same subgroup than HD1, but ruled out the involvement of cry gene content or protoxin activation in the hypertoxicity of this strain. Taking into account the delta-endotoxin/spore ratio for each strain, and by allowing the estimation of the production level per spore, it might be concluded that BLB1 production is the highest, when compared with that of HD1. On the basis of its toxicity, BLB1 could be considered as a strain of great interest and would allow the production of quantities of bioinsecticides at low cost.

Effects ofBacillus thuringiensissubsp.kurstakiHD1 spore-crystal mixture on the adults of egg parasitoidTrichogramma evanescens(Hymenoptera: Trichogrammatidae)

“…Also, the toxin yield was calculated as 16.03 mg/10 5 spores mL ¡1 . Similar results were obtained in a study carried out by Yilmaz et al [7] Also, Saadaoui et al [27] estimated the d-endotoxin production of Btk HD1 as 669 mg mL ¡1 for 10 10 spore L ¡1 .…”

Selection and characterization of Bacillus thuringiensis isolates with a high insecticidal activity against Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…The high toxicity of SUFT01 may be associated with the cry gene copy number and could be a factor in δ-endotoxin overproduction. Other studies also demonstrated that the Bt isolates with greater cry1A gene copy numbers produced more δ-endotoxin than did the reference strain HD1 (SAADAOUI et al, 2009).…”

Evidence of the Involvement of E358, A498 and C571 of a New Cry1Ac δ-endotoxin of Bacillus thuringiensis in its High Insecticidal Activity Against Ephestia kuehniella

“…This strain produces a bipyramidal parasporal crystal exhibiting, against larvae of E. kuehniella, a higher insecticidal activity than that of the reference strain HD1 (B. thuringiensis kurstaki) [16]. The strain HD1CryB, an acrystalliferous strain, was used to produce the Cry1Ac protein of BLB1 and HD1.…”

“…kurstaki strain isolated from a Tunisian soil sample [16]. It showed a d-endotoxin production and an insecticidal activity better than those of commercialized strain HD1.…”