Bioinsecticides from bacteria

In understanding the structure a new bacterial insecticide researchers have uncovered an entirely new way in which cells produce and store toxins to prevent them from harming unintended targets.

The bacteria, Yersinia entomophaga was originally found in the native New Zealand grass grub by Dr Mark Hurst from AgResearch in NZ. The bacteria kill the grubs by secreting an insecticidal protein. The discovery that the bacteria also infect and kill insects such as the diamondback moth that damages crops worldwide, piqued the team’s interest.

Dr Michael Landsberg from the University of Queensland’s (UQ) Institute for Molecular Bioscience has worked with Dr Hurst and had previously determined the overall structure of the bioinsecticidal protein by using the flagship cryo transmission electron microscope in the AMMRF [now Microscopy Australia] at UQ. This study generated an overall 3D structure for the protein and an image of this model features in Microscopy Australia’s touring exhibition, Incredible Inner Space.

In an extension to this research, the team, led by Dr Hurst and Dr Shaun Lott from AgResearch and the University of Auckland, has used the AMMRF [now Microscopy Australia] at UQ and the Australian Synchrotron to build a complete molecular map of this complex protein using the previously elucidated model as a template. As Dr Landsberg explained;

“We showed that the bacteria manufactures a giant, hollow protein shell that encapsulates the toxin, much like a protective canister that is only opened when specific environmental conditions are encountered.”

The importance of these results was recognised by their publication in the journal, Nature.

“The research explains how the bacteria can produce toxins without harming themselves – the toxins are secured in the protein shell and released when they are needed to kill the insect.” Dr Landsberg said the bacteria’s ‘blueprint’ for producing this canister uses a repeating protein sequence that is found abundantly 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.

“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.”

These discoveries have implications for research into human disease as well as for the development of this new class of pesticide.