Bacterial bio-insecticide

When investigating the potential use of bacterial toxins as an insecticide in crops, a team of Australian and New Zealand researchers discovered a new way in which bacteria produce and store toxins.

The team, led by Drs Shaun Lott from AgResearch and the University of Auckland and Mark Hurst from AgResearch, together with Jason Busby from the University of Auckland, Dr Santosh Panjiker from the Australian Synchrotron and Dr Michael Landsberg from The University of Queensland’s Institute for Molecular Bioscience, investigated the biology of Yersinia entomophaga, a bacteria that kills a range of insect species that damage crops.

The bacteria was originally discovered in the native New Zealand grass grub by Dr Hurst. Then it was realised that it also affected insects such as the diamondback moth, which damages crops worldwide.

The ABC toxin complexes produced by certain bacteria have potent insecticidal activity. These complexes comprise at least three proteins (A, B and C), which must assemble to be fully toxic. The carboxy-terminal region of the C protein is the main cytotoxic component.

The researchers observed that the ABC toxin complex in Yersinia entomophaga forms a large hollow structure that encapsulates and sequesters the cytotoxic C-terminal region of the C protein like the protective shell of an egg.

“This explains how the bacteria can produce toxins without harming themselves,” Dr Landsberg explained. “The toxins are secured in the protein shell that is only opened when specific environmental conditions are encountered.”

Dr Landsberg said the bacteria’s ‘blueprint’ for producing this canister uses a repeating protein sequence that is found in large numbers in other bacteria and animals.

“While the sequence encoding the shell is conserved across species, the toxins or other encapsulated molecules can be quite different,” he said of the C-terminal region, which is poorly conserved between different toxin complexes.

“Our studies suggest we may have found a molecular assembly manual that bacterial and animal cells alike use to manufacture a generic canister for the protection of toxic or sensitive molecules.

“This has implications for research into human disease as well as pesticides.”

The findings have been published in Nature.