Engineered gut bacteria killed all tested caterpillars in a lab study

The modified bacterium produced the insect-killing Cry1Ac toxin and colonized both caterpillar guts and tomato leaves in laboratory experiments.

Editorial illustration — not from the study.

Researchers engineered Enterobacter aerogenes, a bacterium found in the gut of Helicoverpa armigera, to produce Cry1Ac, a toxin made by Bacillus thuringiensis. In laboratory tests, the modified bacterium killed up to 100% of exposed larvae, including all larvae in one leaf-treatment test within eight days.

A related version carrying a fluorescent marker colonized caterpillar guts within 48 hours and tomato leaves within 24 hours. The findings support further study of the bacterium as a possible way to deliver insect-killing molecules, but its behavior and safety outside the laboratory remain unknown.

What the modified bacteria did

The researchers introduced two plasmids into Enterobacter aerogenes: one carrying the gene for the Cry1Ac toxin and another producing green fluorescent protein. The fluorescent version colonized Helicoverpa armigera larvae within 48 hours and tomato leaves within 24 hours.

In feeding tests, diets containing 10⁵ to 10⁹ transformed cells produced mortality of 79% to 100% among larvae exposed to engineered E. aerogenes. A Cry1Ac-producing Escherichia coli strain used for comparison produced mortality of 86% to 100% over the same tested cell range.

When leaves were treated with 1.0 × 10⁸ engineered E. aerogenes cells per leaf, the treatment caused 100% larval mortality within 192 hours, or eight days.

Why this could matter

The study provides laboratory evidence that a bacterium naturally associated with H. armigera can be engineered to produce Cry1Ac and establish itself in both caterpillar guts and the tomato leaf environment. That combination could support a pest-management approach in which a symbiotic microbe delivers an insect-killing molecule. The findings are an initial foundation rather than a demonstration that the method is ready for agricultural use.

Evidence and open questions

This was a laboratory study using feeding and leaf-dip bioassays, along with tracking of a fluorescent marker to assess colonization. The engineered bacterium killed exposed Helicoverpa armigera larvae under the tested conditions, but the study did not test environmental persistence, transmission, or biosafety in the field. The researchers say further work is needed under field conditions and other environmentally relevant stresses.

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