Isolation and characterization of a new Bacillus thuringiensis strain with a promising toxicity against Lepidopteran pests

Abstract

Insecticides derived from Bacillus thuringiensis are gaining worldwide importance as environmentally desirable alternatives to chemicals for the control of pests in public health and agriculture. Isolation and characterization of new strains with higher and broader spectrum of activity is an ever growing field. In the present work, a novel Tunisian B. thuringiensis isolate named BLB459 was characterized and electrophoresis assay showed that among a collection of 200 B. thuringiensis strains, the plasmid profile of BLB459 was distinctive. SmaI-PFGE typing confirmed the uniqueness of the DNA pattern of this strain, compared with BUPM95 and HD1 reference strains. PCR and sequencing assays revealed that BLB459 harbored three cry genes (cry30, cry40 and cry54) corresponding to the obtained molecular sizes in the protein pattern. Interestingly, PCR-RFLP assay demonstrated the originality of the BLB459 cry30-type gene compared to the other published cry30 genes. Insecticidal bioassays showed that BLB459 spore-crystal suspension was highly toxic to both Ephestia kuehniella and Spodoptera littoralis with LC50 values of about 64 (53-75) and 80 (69-91) μg of toxin cm(-2), respectively, comparing with that of the commercial strain HD1 used as reference. Important histopathological effects of BLB459 δ-endotoxins on the two tested larvae midguts were detected, traduced by the vacuolization of the apical cells, the damage of microvilli, and the disruption of epithelial cells. These results proved that BLB459 strain could be of a great interest for lepidopteran biocontrol.

Identification of fungi in Tunisian olive orchards: characterization and biological control potential

“…According to previous reports, filamentous fungi, including some of the strains tested in our study as Penicillium chrysogenum F49', Aspergillus ochraceus F57 and Fusarium solani-like F59 may restrict and stop fungal growth. These filamentous fungi such as Aspergillus and Penicillium are known as antimicrobial due to their ability to produce toxic [46]. The susceptibility of Alternaria consortialis to 14 of the fungal isolates as, e.g., Penicillium chrysogenum, Penicillium crustosum, Penicillium pinophilum, and Penicillium polonicum tested in this study is consistent with previous studies reporting the antagonistic activity of antifungal compounds produced by Penicillium sp., (Macropherin A, Atrpinin A, Botryodiplodin and Brefeldin A) which allowed the inhibition of Alternaria sp.…”

“…According to previous reports, filamentous fungi, including some of the strains tested in our study as Penicillium chrysogenum F49’, Aspergillus ochraceus F57 and Fusarium solani- like F59 may restrict and stop fungal growth. These filamentous fungi such as Aspergillus and Penicillium are known as antimicrobial due to their ability to produce toxic secondary metabolites including hydrolytic enzymes such as protease, amylase and lipase [ 46 ].…”

“…The conidial suspension of each fungal strain was determined under the microscope using a Neubauer hemocytometer and adjusted to the cited concentration; a diet with 1 g sterile semolina mixed with 500 μl of sterile water was used as the control. Three replicates were performed for each fungal isolate, including the control [46]. The cumulative mortality was recorded by counting the number of dead larvae after 7 days of incubation under controlled conditions (temperature 22-25°C, 70 ± 10% RH, natural light).…”

Bacillus: A Biological Tool for Crop Improvement through Bio-Molecular Changes in Adverse Environments

“…During later stages of infection, Bacillus spp. crystal protein endotoxin, lipopeptides and polyketides (iturin, fengycin, surfactin, bacillomycin, bacillaene, macrolactin, and difficidin) modify the vacuolization of the cytoplasm, induce vesicle formation, lyse brush border membrane, and degenerate apical membranes, leading to damage of microvilli and finally causing larval death (Ben-Khedher et al, 2015a ; Boukedi et al, 2016 ). Surfactin attaches to the Ca 2+ receptor site and changes the peptide composition in the cellular phospholipid bilayer (Maget-Dana and Ptak, 1995 ), while iturin increases cell membrane permeability via the formation of ion-conducting pores (Maget-Dana and Peypoux, 1994 ).…”

Bioactivity of Bacillus thuringiensis (Bacillales: Bacillaceae) on Diatraea saccharalis (Lepidoptera: Crambidae) eggs

“…14 These microorganisms, as well as their toxins, have been used for controlling various insects, including the sugarcane borer Diatraea saccharalis. 15,16 Bt toxicity is related to protein toxins produced during stages III and V of sporulation. [14][15][16][17][18] Certain strains are able to synthesize up to eight different toxins.…”