Poison comes in small packages
A team of scientists from New Zealand and Australia has discovered the way in which a bacterium packages its toxins in a hollow protein shell and then releases them. They say the discovery could lead to new approaches for bioinsecticides for crop pests and even new medicines.
Diamondback moth
A biological mechanism used by a native New Zealand soil bacterium to release toxins to kill crop pests like the diamondback moth may be used to generate new insecticides.
Insect-killing toxin
The team led by Dr Shaun Lott at the AgResearch Structural Biology Laboratory based at the University of Auckland and Dr Mark Hurst at AgResearch in Lincoln studied how the bacterium Yersinia entomophaga uses an insect-killing toxin to kill crop pests such as grass grubs, diamondback moths and porina caterpillars.
The work was done primarily by AgResearch-funded University of Auckland PhD student Jason Busby as part of his doctoral thesis supervised by Dr Lott and Dr Hurst. The scientists used high-resolution X-ray crystallography and electron microscopy to determine the three-dimensional structure of proteins produced by the bacterium.
New biological mechanism for storing and releasing toxins
They found that the proteins form a relatively large hollow shell, like a protective canister, that releases the toxin only when it encounters specific environmental conditions, such as those found in the gut of crop pests. This explains how the bacterium can produce toxins without harming itself and release them only when needed to kill an insect.
The genetic sequence that provides the blueprint for the shell of repeating proteins is also found in many other species, including animals, and the researchers believe they have discovered a new biological mechanism by which toxins or other sensitive molecules may be stored and released.
Possible applications
Insecticide spraying.
Insecticides are chemicals that are toxic to insects. They are commonly used in agriculture to reduce the number of pests that might damage the crop or pasture. Insecticides are usually specific to insects and should not harm other animals, but scientists are finding that they may, in fact, have a long-term effect on non-target species.
In a joint press release from AgResearch and the University of Auckland, Dr Lott explains that, based on the discovery, scientists may be able to generate new insecticides or even new medicines: “This is a mechanism for delivery and you could pack whatever you want into the shell. You could develop different toxins for use as bioinsecticides or package therapeutic molecules that you want to deliver only in specific conditions.”
The bacterium Yersinia entomophaga, a native New Zealand soil bacterium that makes a potent insect-killing toxin, was originally discovered in the native New Zealand grass grub by Dr Hurst. It was subsequently found to affect other insect pests such as the diamondback moth, which damages crop pests worldwide, highlighting its potential for use as a new form of insecticide.
The study also involved researchers at the Australian Synchrotron and The University of Queensland.
The research was published online ahead of print in August 2013 by the journal Nature.
Activity idea
The scientists in this news article used electron microscopy in their research. Your students may like to learn more about electron microscopes and what they are used for.
Types of electron microscope
