Abstract
Bacillus thuringiensis has been extensively used for the biological control of insect pests. Nematicidal B. thuringiensis strains have also been identified; however, virulence factors of such strains are poorly investigated. Here, we describe virulence factors of the nematicidal B. thuringiensis 4A4 strain, using the model nematodes Pristionchus pacificus and Caenorhabditis elegans. We show that B. thuringiensis 4A4 kills both nematodes via intestinal damage. Whole genome sequencing of B. thuringiensis 4A4 identified Cry21Ha, Cry1Ba, Vip1/Vip2 and β-exotoxin as potential nematicidal factors. Only Cry21Ha showed toxicity to C. elegans, while neither Cry nor Vip toxins were active against P. pacificus, when expressed in E. coli. Purified crystals also failed to intoxicate P. pacificus, while autoclaved spore-crystal mixture of B. thuringiensis 4A4 retained toxicity, suggesting that primary β-exotoxin is responsible for P. pacificus killing. In support of this, we found that a β-exotoxin-deficient variant of B. thuringiensis 4A4, generated by plasmid curing lost virulence to the nematodes. Thus, using two model nematodes we revealed virulence factors of the nematicidal strain B. thuringiensis 4A4 and showed the multifactorial nature of its virulence.
Highlights
The Spore-forming bacterium Bacillus thuringiensis is successfully used for the biological control of agricultural pests [1]
To identify B. thuringiensis strains pathogenic to P. pacificus, we exposed this nematode to several representative strains of different B. thuringiensis serovars and scored survival
We found that both, C. elegans and P. pacificus strongly avoided B. thuringiensis 4A4 in chemotaxis assays (Figure 4A), preferentially moving towards an
Summary
The Spore-forming bacterium Bacillus thuringiensis is successfully used for the biological control of agricultural pests [1]. Some B. thuringiensis strains secrete toxins during vegetative growth, which are called vegetative insecticidal proteins (Vip) [10,11,12]. Caenorhabditis elegans was used as the only model to study bacterial nematicidal factors and nematode defense mechanisms [16,18,19,20,21]. Given that P. pacificus is resistant to some Cry toxins that have been tested, B. thuringiensis strains pathogenic to P. pacificus will very likely rely on mechanisms distinct from. P. pacificus resistance to Cry toxins facilitates the use of this nematode to study B. thuringiensis nematicidal virulence factors distinct from Cry toxins. Functional characterization of these toxins suggests a multifactorial nature of B. thuringiensis 4A4 virulence to nematodes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
