Journal
TOXINS
Volume 13, Issue 11, Pages -Publisher
MDPI
DOI: 10.3390/toxins13110746
Keywords
immunotoxicology; ROS; oxidative stress; antioxidants; midgut microbiome; biocontrol; Leptinotarsa decemlineata; plant protection
Categories
Funding
- Russian Science Foundation [19-16-00019]
- President RF [? MK-318.2020.11]
- Russian Science Foundation [19-16-00019] Funding Source: Russian Science Foundation
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The insect integument acts as a barrier to disease-causing agents, but Bacillus thuringiensis (Bt) must overcome gut-based defences to establish infection. Bt spores and Cry3A toxins have negative impacts on larval health, activating the insect detoxification system and causing tissue damage.
The insect integument (exoskeleton) is an effective physiochemical barrier that limits disease-causing agents to a few portals of entry, including the gastrointestinal and reproductive tracts. The bacterial biopesticide Bacillus thuringiensis (Bt) enters the insect host via the mouth and must thwart gut-based defences to make its way into the body cavity (haemocoel) and establish infection. We sought to uncover the main antibacterial defences of the midgut and the pathophysiological features of Bt in a notable insect pest, the Colorado potato beetle Leptinotarsa decemlineata (CPB). Exposing the beetles to both Bt spores and their Cry3A toxins (crystalline delta-endotoxins) via oral inoculation led to higher mortality levels when compared to either spores or Cry3A toxins alone. Within 12 h post-exposure, Cry3A toxins caused a 1.5-fold increase in the levels of reactive oxygen species (ROS) and malondialdehyde (lipid peroxidation) within the midgut - key indicators of tissue damage. When Cry3A toxins are combined with spores, gross redox imbalance and 'oxidation stress' is apparent in beetle larvae. The insect detoxification system is activated when Bt spores and Cry3A toxins are administered alone or in combination to mitigate toxicosis, in addition to elevated mRNA levels of candidate defence genes (pattern-recognition receptor, stress-regulation, serine proteases, and prosaposin-like protein). The presence of bacterial spores and/or Cry3A toxins coincides with subtle changes in microbial community composition of the midgut, such as decreased Pseudomonas abundance at 48 h post inoculation. Both Bt spores and Cry3A toxins have negative impacts on larval health, and when combined, likely cause metabolic derangement, due to multiple tissue targets being compromised.
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