Diversity of Bacillus thuringiensis Strains From Qatar as Shown by Crystal Morphology, δ-Endotoxins and Cry Gene Content

Abstract

Bacillus thuringiensis (Bt) based insecticidal formulations have been recognized as one of the most successful, environmentally safe and sustainable method of controlling insect pests. Research teams worldwide are in search of Bt diversity giving more choices of bio-insecticides and alternatives to address insect resistance. In fact, there are many unexplored ecologies that could harbor novel Bt strains. This study is the first initiative to explore Bt strain diversity in Qatar. A collection of 700 Bt isolates was constructed. Scanning electron microscopy of Bt crystals showed different crystal forms, with a high abundance of spherical crystals compared to the bipyramidal ones. Among the spherical crystals, four different morphologies were observed. The δ-endotoxin content of parasporal crystals from each Bt isolate revealed that there are 16 different protein profiles among the isolates of the collection. On the other hand, plasmid pattern analysis showed seven different plasmid profiles. Their insecticidal activity was predicted by exploring the δ-endotoxin coding genes and conducting qualitative insecticidal bioassays. 19 smooth spherical crystal producing isolates have been identified that could be possible candidates for endotoxin production targeting Dipteran insects. Another group of 259 isolates producing bipyramidal and cuboidal crystals could target Lepidopteran and Coleopteran insects. The remaining 422 isolates have novel profiles. In conclusion, Qatari soil ecology provides a good collection and diversity of Bt isolates. In addition to strains harboring genes encoding common endotoxins, the majority are different and very promising for the search of novel insecticidal endotoxins.

Selection of Bacillus thuringiensis strains in citrus and their pathogenicity to Diaphorina citri (Hemiptera: Liviidae) nymphs

“…For the first time, we confirmed the ability of Bt strains to translocate from roots to shoots in citrus seedlings, and cause high mortality of D. citri nymphs feeding on them. Furthermore, PCR allows rapid identification of Bt strains and toxin genes, and it has been successfully used in this and other studies (Monnerat et al ., ; Praça et al ., ; Nair et al ., ). PCR of Bt colonies with the specific primers used in this work allowed to unequivocally confirm the identity of the strain, and also confirmed the cause of nymphal mortality observed in our assays.…”

Silicon-Solubilizing Media and Its Implication for Characterization of Bacteria to Mitigate Biotic Stress

“…Systematics of different Si solubilizers was performed through 16S rDNA sequencing as described earlier (Nautiyal et al, 2013a). In brief 16S rRNA gene was amplified using forward 27F (5′-AGAGTTTGATCCTGGCTCAG-3′) and reverse 1492R (5′-AAGGAGGTGATCCAGCCGCA-3′) primers under standard PCR conditions (Initial denaturation at 94°C for 5 min, 30 cycles of denaturation at 94°C for 1 min, annealing at 50°C for 40 s, extension at 72°C for 90 s, and final extension at 72°C for 7 min) (Weisburg et al, 1991;Cui et al, 2001;Nair et al, 2018). Purified PCR product (~1.4 kb) was sequenced at Central Instrument Facility at National Botanical Research Institute, Lucknow using ABI 3730XL capillary DNA sequencer (50 cm capillary).…”

Insecticidal activity of the metabolites of sand soil bacteria in Northern Senegal

“…Species of the Bacillus genus are generally also found in soil, and they have many benefits 38 , especially for crop improvement, due to the resulting biomolecular changes in adverse environments 39 , defense against vectors of infectious diseases 40 and antimicrobial properties 13 . For this purpose, different studies have been carried out involving the isolation of bacteria from the soil for biological effects research 38,14,16,13 . A study (1998) was carried out in Senegal to search for strains of B. thuringiensis and B. sphaericus useful for the control of malaria, which revealed that 27/203 (13.3%) of strains were active 41 , currently, many studies report resistance to the latter species 42,43,44 , and we must seek better solutions.…”

“…Several projects have studied large collections of Bacillus species to identify direct biological activity, including insecticidal activity 13,14,15,16 , and numerous other Bacillus spp. show high toxicity against dipterans such as Bacillus circulans 45 and Brevibacillus laterosporus 46,47 .…”