Microbial biopesticides: A discovery to produce insecticidal toxins without spore formation

Bacillus thuringiensis, commonly known as Bt, is a spore-forming bacterium that produces toxins that are particularly effective against many lepidopteran crop pests such as the European corn borer and the cotton bollworm. Bt held 74% of the market share for bacterial biopesticides in 2024. Since the 1980s, studies have shown a close correlation between the production of these crystal-forming Cry toxins and the sporulation process of Bt strains.

Scientists at INRAE have challenged this paradigm by demonstrating that the VipR regulator controls the production of these Cry toxins in a parent strain of commercial strains. Using modified strains that do not form spores, the research team was able to show that these Cry toxins are produced under the control of VipR independently from the sporulation process.

The scientists conducted a complementary genomic study revealing that this regulator is indeed present in the Bt strains used in the most widely sold biopesticides, suggesting that this mechanism for Cry toxin production can be generalized to these strains.

The researchers had previously shown that the VipR regulator also controls the production of Vip3, an insecticidal toxin also produced by the DiPel® strain, which is the most widely used commercially. This Vip3 toxin is not found in biopesticide formulations due to its early production (before sporulation) and its lack of crystallization.

The simultaneous production of both Cry and Vip3 toxins in non-sporulating bacteria will broaden the insecticidal spectrum of biopesticide formulations while also lowering the risk of insects developing resistance.

The ability to produce insecticidal toxins without sporulation prevents spores being dispersed into the environment. This would be of benefit from an environmental and public health perspective as it would limit the risk of foodborne illness associated with the phylogenetic proximity of Bt to Bacillus cereus.

After identifying the VipR regulator and the regulating sequences in non-sporulating strains, the researchers filed an initial patent for the production of proteins of interest in this genetic context. A second patent is currently being filed for the development of a genetically modified, non-sporulating Bt strain that is not lysed¹. This means the toxins produced by the strain are retained within the bacterial cell, which limits UV degradation and allows for prolonged toxin activity. More broadly, this research paves the way for the genetic improvement of Bt strains used as commercial biopesticides. 

1. Breakdown of the cell membrane caused by an agent (physical, chemical or biological) resulting in the cell’s death.