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

Kavita Nair,Samir Jaoua,Roda Al-Thani,Dhabia Al-Thani,Talaat Ahmed,Fatima Al-Yafei

doi:10.3389/fmicb.2018.00708

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.

Highlights

Bacillus thuringiensis (Bt) is an entomopathogenic, rod shaped, Gram positive, spore-forming and aerobic bacterium found usually in soil, grain dusts, dead insects and water (Lambert and Peferoen, 1992)
Characterization of Bt Isolates Based on Crystal Morphology and Phylogeny
The observation of crystal forms of the 700 isolates carried out by light microscope allowed the collection to be classified into two main classes.:441 isolates producing spherical crystals and 259 isolates producing bipyramidal and cuboidal crystals

Summary

Introduction

Bacillus thuringiensis (Bt) is an entomopathogenic, rod shaped, Gram positive, spore-forming and aerobic bacterium found usually in soil, grain dusts, dead insects and water (Lambert and Peferoen, 1992). Bt is considered the most successful bioinsecticidal alternative available to man today, owing to its toxicity toward a broad range of insect pests such as Dipteran, Lepidopteran and Coleopteran (Federici et al, 2006; Lacey et al, 2015). Based on their serotype and phylogenetic features, Bt is classified into subspecies; which are further classified into serotypes and Exploration of Qatari Bacillus thuringiensis strains (Seifinejad et al, 2008). Bt israelensis (Bti) produces a combination of endotoxins (Cry) and hemolytic proteins (Cyt) during sporulation stage and crystallize them in a spherical form. Research teams worldwide are constantly screening different ecologies to find such novel Bt isolates (Campanini et al, 2012; Soares-da-Silva et al, 2015; El-Kersh et al, 2016)

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