A novel Bacillus thuringiensis gene encoding a Spodoptera exigua-specific crystal protein

Area of Science:

• Microbiology
• Molecular Biology
• Insect Toxicology

Background:

• Bacillus thuringiensis crystal proteins (Cry) are crucial for insecticidal activity.
• Previous research identified CryIC as toxic to Spodoptera species, but other Cry subclasses showed limited efficacy against certain pests.
• The diversity of Cry proteins is key to developing targeted pest management solutions.

Purpose of the Study:

• To identify novel crystal protein genes in Bacillus thuringiensis strains.
• To characterize the nucleotide sequence and insecticidal activity of a newly discovered gene.
• To determine if the novel gene represents a new Cry protein subclass.

Main Methods:

• Screening of 25 Bacillus thuringiensis strains using a cryIC-derived nucleotide probe.
• Cloning and nucleotide sequencing of a putative crystal protein gene (BtXI) from strain 4F1.
• Western immunoblot analysis to detect the expressed polypeptide.
• Toxicity assays against various lepidopteran larvae (Spodoptera exigua, Heliothis virescens, Mamestra brassicae, Pieris brassicae).

Main Results:

• A novel crystal protein gene, BtXI, was identified and cloned.
• BtXI shares sequence homology with both CryIA and CryIC subclasses, suggesting a unique structure.
• Recombinant BtXI demonstrated high toxicity against Spodoptera exigua larvae, comparable to CryIC.
• No significant toxicity was observed against Heliothis virescens, Mamestra brassicae, or Pieris brassicae.

Conclusions:

• The novel gene BtXI represents a new Cry protein subclass, proposed as CryIE.
• CryIE exhibits specific toxicity against Spodoptera exigua, broadening the insecticidal spectrum of Bacillus thuringiensis.
• This discovery contributes to understanding Cry protein diversity and developing targeted biopesticides.