Review Paper:
Bacillus thuringiensis
Cry and Cyt Toxins: Mechanisms of Action, Resistance Management and Impact on Host
Immune Responses
Bangaru Naidu Thaddi
Res. J. Chem. Environ.; Vol. 29(4); 101-110;
doi: https://doi.org/10.25303/294rjce1010110; (2025)
Abstract
Bacillus thuringiensis (Bt) is a pioneering biopesticide known for its potent insecticidal
proteins, particularly Cry and Cyt toxins which have transformed agricultural pest
management worldwide. As a naturally occurring bacterium, Bt is favored for its
environmentally friendly profile and high specificity toward target insect pests,
significantly reducing reliance on synthetic chemical pesticides.
This review focused on the mechanisms of action of Bt toxins, their specificity
and the implications for pest management strategies. Cry toxins are produced as
inactive protoxins that undergo proteolytic activation in the alkaline environment
of the insect midgut. This activation triggers a conformational change, enabling
the protoxins to bind to specific receptors on midgut epithelial cells such as cadherins,
aminopeptidases and alkaline phosphatases. These binding initiates biological events
that lead to pore formation, cell lysis and ultimately, insect mortality. The specificity
of Cry toxins largely depends on their interactions with these receptors, which
vary among different insect species. In contrast, Cyt toxins employ a different
mechanism by directly interacting with lipid bilayers to form pores, allowing them
to target a broader spectrum of insect pests, including those resistant to Cry toxins.
Recent research has shed light on the structural details of toxin-receptor interactions
and pore formation mechanisms, facilitating the development of novel Bt toxins with
enhanced efficacy and broader activity spectra.
Insights from genomic studies on resistance mechanisms have revealed critical information
about receptor gene mutations and midgut protease activity alterations, essential
for developing targeted solutions against resistance. The environmental and non-target
effects of Bt toxins are also crucial considerations. Current research indicates
that Bt toxins generally have minimal adverse impacts on beneficial insects, soil
microbiota and aquatic ecosystems, underscoring their ecological safety profile.
