Australasian Science: Australia's authority on science since 1938

Biocanisters of Toxins

By Stephen Luntz

The discovery of the mechanism by which certain bacteria poison insects could prove invaluable for both the fight against pest species and for future medical advances.

Yersinia entomophoga is a bacterium that kills many pest insect species. However, until a New Zealand/Australian collaboration published its findings in Nature it was not known how they did this without poisoning themselves.

“We showed 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,” says Dr Michael Landsberg of the University of Queensland’s Institute for Molecular Bioscience. “This explains how the bacteria can produce toxins without harming themselves – the toxins are secured in the protein shell and released at an appropriate time, which is what kills the insect.”

Landsberg says part of the circumstance for the opening of the shell is encountering the acidic conditions in the insect gut, but since acidic environments occur elsewhere there is a second component he can’t discuss while awaiting publication of this further aspect of the research.

Killing of the host isn’t smart for parasites, but Landsberg says the trait appears in a related species that forms a symbiotic relationship with nematode worms. When the toxin kills its host both the worm and the bacterium feed on the body before “reassimilating and moving on to find new prey,” Landsberg says. Y. entomophoga has conserved this capacity.

The canister-building DNA exists not only in bacteria but also in animals, including humans. “In human neurons, the canister preserves an important signalling molecule that needs to be released at the right time,” Landsberg says.

Y. entomophoga does not have negative effects on humans, but its cousin Y. pestis is thought to be responsible for the black plague. It was discovered killing a New Zealand beetle, but it has now been shown that it eliminates the common vegetable pest the diamondback moth.

“Currently 90% of the global biotech market for insecticides is from Bacillus thuringiensis (Bt) either sprayed on the plant or genetically incorporated into the crop,” Landsberg says. “Both of these are potential routes of delivery. The advantage is that the toxin is not persistent so it does not bioaccumulate.” Alternative pesticides could delay resistance to Bt.

Landsberg also notes that “the canisters can be made in many shapes and sizes, and might be able to package drugs that you only want to release under specific conditions”.